1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 1708 1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760 1761 1762 1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774 1775 1776 1777 1778 1779 1780 1781 1782 1783 1784 1785 1786 1787 1788 1789 1790 1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805 1806 1807 1808 1809 1810 1811 1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 1860 1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871 1872 1873 1874 1875 1876 1877 1878 1879 1880 1881 1882 1883 1884 1885 1886 1887 1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 2037 2038 2039 2040 2041 2042 2043 2044 2045 2046 2047 2048 2049 2050 2051 2052 2053 2054 2055 2056 2057 2058 2059 2060 2061 2062 2063 2064 2065 2066 2067 2068 2069 2070 2071 2072 2073 2074 2075 2076 2077 2078 2079 2080 2081 2082 2083 2084 2085 2086 2087 2088 2089 2090 2091 2092 2093 2094 2095 2096 2097 2098 2099 2100 2101 2102 2103 2104 2105 2106 2107 2108 2109 2110 2111 2112 2113 2114 2115 2116 2117 2118 2119 2120 2121 2122 2123 2124 2125 2126 2127 2128 2129 2130 2131 2132 2133 2134 2135 2136 2137 2138 2139 2140 2141 2142 2143 2144 2145 2146 2147 2148 2149 2150 2151 2152 2153 2154 2155 2156 2157 2158 2159
//! Single-threaded reference-counting pointers. 'Rc' stands for 'Reference //! Counted'. //! //! The type [`Rc<T>`][`Rc`] provides shared ownership of a value of type `T`, //! allocated in the heap. Invoking [`clone`][clone] on [`Rc`] produces a new //! pointer to the same value in the heap. When the last [`Rc`] pointer to a //! given value is destroyed, the pointed-to value is also destroyed. //! //! Shared references in Rust disallow mutation by default, and [`Rc`] //! is no exception: you cannot generally obtain a mutable reference to //! something inside an [`Rc`]. If you need mutability, put a [`Cell`] //! or [`RefCell`] inside the [`Rc`]; see [an example of mutability //! inside an Rc][mutability]. //! //! [`Rc`] uses non-atomic reference counting. This means that overhead is very //! low, but an [`Rc`] cannot be sent between threads, and consequently [`Rc`] //! does not implement [`Send`][send]. As a result, the Rust compiler //! will check *at compile time* that you are not sending [`Rc`]s between //! threads. If you need multi-threaded, atomic reference counting, use //! [`sync::Arc`][arc]. //! //! The [`downgrade`][downgrade] method can be used to create a non-owning //! [`Weak`] pointer. A [`Weak`] pointer can be [`upgrade`][upgrade]d //! to an [`Rc`], but this will return [`None`] if the value has //! already been dropped. //! //! A cycle between [`Rc`] pointers will never be deallocated. For this reason, //! [`Weak`] is used to break cycles. For example, a tree could have strong //! [`Rc`] pointers from parent nodes to children, and [`Weak`] pointers from //! children back to their parents. //! //! `Rc<T>` automatically dereferences to `T` (via the [`Deref`] trait), //! so you can call `T`'s methods on a value of type [`Rc<T>`][`Rc`]. To avoid name //! clashes with `T`'s methods, the methods of [`Rc<T>`][`Rc`] itself are associated //! functions, called using function-like syntax: //! //! ``` //! use std::rc::Rc; //! let my_rc = Rc::new(()); //! //! Rc::downgrade(&my_rc); //! ``` //! //! [`Weak<T>`][`Weak`] does not auto-dereference to `T`, because the value may have //! already been destroyed. //! //! # Cloning references //! //! Creating a new reference from an existing reference counted pointer is done using the //! `Clone` trait implemented for [`Rc<T>`][`Rc`] and [`Weak<T>`][`Weak`]. //! //! ``` //! use std::rc::Rc; //! let foo = Rc::new(vec![1.0, 2.0, 3.0]); //! // The two syntaxes below are equivalent. //! let a = foo.clone(); //! let b = Rc::clone(&foo); //! // a and b both point to the same memory location as foo. //! ``` //! //! The `Rc::clone(&from)` syntax is the most idiomatic because it conveys more explicitly //! the meaning of the code. In the example above, this syntax makes it easier to see that //! this code is creating a new reference rather than copying the whole content of foo. //! //! # Examples //! //! Consider a scenario where a set of `Gadget`s are owned by a given `Owner`. //! We want to have our `Gadget`s point to their `Owner`. We can't do this with //! unique ownership, because more than one gadget may belong to the same //! `Owner`. [`Rc`] allows us to share an `Owner` between multiple `Gadget`s, //! and have the `Owner` remain allocated as long as any `Gadget` points at it. //! //! ``` //! use std::rc::Rc; //! //! struct Owner { //! name: String, //! // ...other fields //! } //! //! struct Gadget { //! id: i32, //! owner: Rc<Owner>, //! // ...other fields //! } //! //! fn main() { //! // Create a reference-counted `Owner`. //! let gadget_owner: Rc<Owner> = Rc::new( //! Owner { //! name: "Gadget Man".to_string(), //! } //! ); //! //! // Create `Gadget`s belonging to `gadget_owner`. Cloning the `Rc<Owner>` //! // value gives us a new pointer to the same `Owner` value, incrementing //! // the reference count in the process. //! let gadget1 = Gadget { //! id: 1, //! owner: Rc::clone(&gadget_owner), //! }; //! let gadget2 = Gadget { //! id: 2, //! owner: Rc::clone(&gadget_owner), //! }; //! //! // Dispose of our local variable `gadget_owner`. //! drop(gadget_owner); //! //! // Despite dropping `gadget_owner`, we're still able to print out the name //! // of the `Owner` of the `Gadget`s. This is because we've only dropped a //! // single `Rc<Owner>`, not the `Owner` it points to. As long as there are //! // other `Rc<Owner>` values pointing at the same `Owner`, it will remain //! // allocated. The field projection `gadget1.owner.name` works because //! // `Rc<Owner>` automatically dereferences to `Owner`. //! println!("Gadget {} owned by {}", gadget1.id, gadget1.owner.name); //! println!("Gadget {} owned by {}", gadget2.id, gadget2.owner.name); //! //! // At the end of the function, `gadget1` and `gadget2` are destroyed, and //! // with them the last counted references to our `Owner`. Gadget Man now //! // gets destroyed as well. //! } //! ``` //! //! If our requirements change, and we also need to be able to traverse from //! `Owner` to `Gadget`, we will run into problems. An [`Rc`] pointer from `Owner` //! to `Gadget` introduces a cycle between the values. This means that their //! reference counts can never reach 0, and the values will remain allocated //! forever: a memory leak. In order to get around this, we can use [`Weak`] //! pointers. //! //! Rust actually makes it somewhat difficult to produce this loop in the first //! place. In order to end up with two values that point at each other, one of //! them needs to be mutable. This is difficult because [`Rc`] enforces //! memory safety by only giving out shared references to the value it wraps, //! and these don't allow direct mutation. We need to wrap the part of the //! value we wish to mutate in a [`RefCell`], which provides *interior //! mutability*: a method to achieve mutability through a shared reference. //! [`RefCell`] enforces Rust's borrowing rules at runtime. //! //! ``` //! use std::rc::Rc; //! use std::rc::Weak; //! use std::cell::RefCell; //! //! struct Owner { //! name: String, //! gadgets: RefCell<Vec<Weak<Gadget>>>, //! // ...other fields //! } //! //! struct Gadget { //! id: i32, //! owner: Rc<Owner>, //! // ...other fields //! } //! //! fn main() { //! // Create a reference-counted `Owner`. Note that we've put the `Owner`'s //! // vector of `Gadget`s inside a `RefCell` so that we can mutate it through //! // a shared reference. //! let gadget_owner: Rc<Owner> = Rc::new( //! Owner { //! name: "Gadget Man".to_string(), //! gadgets: RefCell::new(vec![]), //! } //! ); //! //! // Create `Gadget`s belonging to `gadget_owner`, as before. //! let gadget1 = Rc::new( //! Gadget { //! id: 1, //! owner: Rc::clone(&gadget_owner), //! } //! ); //! let gadget2 = Rc::new( //! Gadget { //! id: 2, //! owner: Rc::clone(&gadget_owner), //! } //! ); //! //! // Add the `Gadget`s to their `Owner`. //! { //! let mut gadgets = gadget_owner.gadgets.borrow_mut(); //! gadgets.push(Rc::downgrade(&gadget1)); //! gadgets.push(Rc::downgrade(&gadget2)); //! //! // `RefCell` dynamic borrow ends here. //! } //! //! // Iterate over our `Gadget`s, printing their details out. //! for gadget_weak in gadget_owner.gadgets.borrow().iter() { //! //! // `gadget_weak` is a `Weak<Gadget>`. Since `Weak` pointers can't //! // guarantee the value is still allocated, we need to call //! // `upgrade`, which returns an `Option<Rc<Gadget>>`. //! // //! // In this case we know the value still exists, so we simply //! // `unwrap` the `Option`. In a more complicated program, you might //! // need graceful error handling for a `None` result. //! //! let gadget = gadget_weak.upgrade().unwrap(); //! println!("Gadget {} owned by {}", gadget.id, gadget.owner.name); //! } //! //! // At the end of the function, `gadget_owner`, `gadget1`, and `gadget2` //! // are destroyed. There are now no strong (`Rc`) pointers to the //! // gadgets, so they are destroyed. This zeroes the reference count on //! // Gadget Man, so he gets destroyed as well. //! } //! ``` //! //! [`Rc`]: struct.Rc.html //! [`Weak`]: struct.Weak.html //! [clone]: ../../std/clone/trait.Clone.html#tymethod.clone //! [`Cell`]: ../../std/cell/struct.Cell.html //! [`RefCell`]: ../../std/cell/struct.RefCell.html //! [send]: ../../std/marker/trait.Send.html //! [arc]: ../../std/sync/struct.Arc.html //! [`Deref`]: ../../std/ops/trait.Deref.html //! [downgrade]: struct.Rc.html#method.downgrade //! [upgrade]: struct.Weak.html#method.upgrade //! [`None`]: ../../std/option/enum.Option.html#variant.None //! [mutability]: ../../std/cell/index.html#introducing-mutability-inside-of-something-immutable #![stable(feature = "rust1", since = "1.0.0")] #[cfg(not(test))] use crate::boxed::Box; #[cfg(test)] use std::boxed::Box; use core::any::Any; use core::borrow; use core::cell::Cell; use core::cmp::Ordering; use core::fmt; use core::hash::{Hash, Hasher}; use core::intrinsics::abort; use core::marker::{self, Unpin, Unsize, PhantomData}; use core::mem::{self, align_of, align_of_val, forget, size_of_val}; use core::ops::{Deref, Receiver, CoerceUnsized, DispatchFromDyn}; use core::pin::Pin; use core::ptr::{self, NonNull}; use core::slice::from_raw_parts_mut; use core::convert::From; use core::usize; use crate::alloc::{Global, Alloc, Layout, box_free, handle_alloc_error}; use crate::string::String; use crate::vec::Vec; struct RcBox<T: ?Sized> { strong: Cell<usize>, weak: Cell<usize>, value: T, } /// A single-threaded reference-counting pointer. 'Rc' stands for 'Reference /// Counted'. /// /// See the [module-level documentation](./index.html) for more details. /// /// The inherent methods of `Rc` are all associated functions, which means /// that you have to call them as e.g., [`Rc::get_mut(&mut value)`][get_mut] instead of /// `value.get_mut()`. This avoids conflicts with methods of the inner /// type `T`. /// /// [get_mut]: #method.get_mut #[cfg_attr(not(test), lang = "rc")] #[stable(feature = "rust1", since = "1.0.0")] pub struct Rc<T: ?Sized> { ptr: NonNull<RcBox<T>>, phantom: PhantomData<T>, } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized> !marker::Send for Rc<T> {} #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized> !marker::Sync for Rc<T> {} #[unstable(feature = "coerce_unsized", issue = "27732")] impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Rc<U>> for Rc<T> {} #[unstable(feature = "dispatch_from_dyn", issue = "0")] impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Rc<U>> for Rc<T> {} impl<T> Rc<T> { /// Constructs a new `Rc<T>`. /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let five = Rc::new(5); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn new(value: T) -> Rc<T> { Rc { // there is an implicit weak pointer owned by all the strong // pointers, which ensures that the weak destructor never frees // the allocation while the strong destructor is running, even // if the weak pointer is stored inside the strong one. ptr: Box::into_raw_non_null(box RcBox { strong: Cell::new(1), weak: Cell::new(1), value, }), phantom: PhantomData, } } /// Constructs a new `Pin<Rc<T>>`. If `T` does not implement `Unpin`, then /// `value` will be pinned in memory and unable to be moved. #[stable(feature = "pin", since = "1.33.0")] pub fn pin(value: T) -> Pin<Rc<T>> { unsafe { Pin::new_unchecked(Rc::new(value)) } } /// Returns the contained value, if the `Rc` has exactly one strong reference. /// /// Otherwise, an [`Err`][result] is returned with the same `Rc` that was /// passed in. /// /// This will succeed even if there are outstanding weak references. /// /// [result]: ../../std/result/enum.Result.html /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let x = Rc::new(3); /// assert_eq!(Rc::try_unwrap(x), Ok(3)); /// /// let x = Rc::new(4); /// let _y = Rc::clone(&x); /// assert_eq!(*Rc::try_unwrap(x).unwrap_err(), 4); /// ``` #[inline] #[stable(feature = "rc_unique", since = "1.4.0")] pub fn try_unwrap(this: Self) -> Result<T, Self> { if Rc::strong_count(&this) == 1 { unsafe { let val = ptr::read(&*this); // copy the contained object // Indicate to Weaks that they can't be promoted by decrementing // the strong count, and then remove the implicit "strong weak" // pointer while also handling drop logic by just crafting a // fake Weak. this.dec_strong(); let _weak = Weak { ptr: this.ptr }; forget(this); Ok(val) } } else { Err(this) } } } impl<T: ?Sized> Rc<T> { /// Consumes the `Rc`, returning the wrapped pointer. /// /// To avoid a memory leak the pointer must be converted back to an `Rc` using /// [`Rc::from_raw`][from_raw]. /// /// [from_raw]: struct.Rc.html#method.from_raw /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let x = Rc::new(10); /// let x_ptr = Rc::into_raw(x); /// assert_eq!(unsafe { *x_ptr }, 10); /// ``` #[stable(feature = "rc_raw", since = "1.17.0")] pub fn into_raw(this: Self) -> *const T { let ptr: *const T = &*this; mem::forget(this); ptr } /// Constructs an `Rc` from a raw pointer. /// /// The raw pointer must have been previously returned by a call to a /// [`Rc::into_raw`][into_raw]. /// /// This function is unsafe because improper use may lead to memory problems. For example, a /// double-free may occur if the function is called twice on the same raw pointer. /// /// [into_raw]: struct.Rc.html#method.into_raw /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let x = Rc::new(10); /// let x_ptr = Rc::into_raw(x); /// /// unsafe { /// // Convert back to an `Rc` to prevent leak. /// let x = Rc::from_raw(x_ptr); /// assert_eq!(*x, 10); /// /// // Further calls to `Rc::from_raw(x_ptr)` would be memory unsafe. /// } /// /// // The memory was freed when `x` went out of scope above, so `x_ptr` is now dangling! /// ``` #[stable(feature = "rc_raw", since = "1.17.0")] pub unsafe fn from_raw(ptr: *const T) -> Self { let offset = data_offset(ptr); // Reverse the offset to find the original RcBox. let fake_ptr = ptr as *mut RcBox<T>; let rc_ptr = set_data_ptr(fake_ptr, (ptr as *mut u8).offset(-offset)); Rc { ptr: NonNull::new_unchecked(rc_ptr), phantom: PhantomData, } } /// Consumes the `Rc`, returning the wrapped pointer as `NonNull<T>`. /// /// # Examples /// /// ``` /// #![feature(rc_into_raw_non_null)] /// /// use std::rc::Rc; /// /// let x = Rc::new(10); /// let ptr = Rc::into_raw_non_null(x); /// let deref = unsafe { *ptr.as_ref() }; /// assert_eq!(deref, 10); /// ``` #[unstable(feature = "rc_into_raw_non_null", issue = "47336")] #[inline] pub fn into_raw_non_null(this: Self) -> NonNull<T> { // safe because Rc guarantees its pointer is non-null unsafe { NonNull::new_unchecked(Rc::into_raw(this) as *mut _) } } /// Creates a new [`Weak`][weak] pointer to this value. /// /// [weak]: struct.Weak.html /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let five = Rc::new(5); /// /// let weak_five = Rc::downgrade(&five); /// ``` #[stable(feature = "rc_weak", since = "1.4.0")] pub fn downgrade(this: &Self) -> Weak<T> { this.inc_weak(); // Make sure we do not create a dangling Weak debug_assert!(!is_dangling(this.ptr)); Weak { ptr: this.ptr } } /// Gets the number of [`Weak`][weak] pointers to this value. /// /// [weak]: struct.Weak.html /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let five = Rc::new(5); /// let _weak_five = Rc::downgrade(&five); /// /// assert_eq!(1, Rc::weak_count(&five)); /// ``` #[inline] #[stable(feature = "rc_counts", since = "1.15.0")] pub fn weak_count(this: &Self) -> usize { this.weak() - 1 } /// Gets the number of strong (`Rc`) pointers to this value. /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let five = Rc::new(5); /// let _also_five = Rc::clone(&five); /// /// assert_eq!(2, Rc::strong_count(&five)); /// ``` #[inline] #[stable(feature = "rc_counts", since = "1.15.0")] pub fn strong_count(this: &Self) -> usize { this.strong() } /// Returns `true` if there are no other `Rc` or [`Weak`][weak] pointers to /// this inner value. /// /// [weak]: struct.Weak.html #[inline] fn is_unique(this: &Self) -> bool { Rc::weak_count(this) == 0 && Rc::strong_count(this) == 1 } /// Returns a mutable reference to the inner value, if there are /// no other `Rc` or [`Weak`][weak] pointers to the same value. /// /// Returns [`None`] otherwise, because it is not safe to /// mutate a shared value. /// /// See also [`make_mut`][make_mut], which will [`clone`][clone] /// the inner value when it's shared. /// /// [weak]: struct.Weak.html /// [`None`]: ../../std/option/enum.Option.html#variant.None /// [make_mut]: struct.Rc.html#method.make_mut /// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let mut x = Rc::new(3); /// *Rc::get_mut(&mut x).unwrap() = 4; /// assert_eq!(*x, 4); /// /// let _y = Rc::clone(&x); /// assert!(Rc::get_mut(&mut x).is_none()); /// ``` #[inline] #[stable(feature = "rc_unique", since = "1.4.0")] pub fn get_mut(this: &mut Self) -> Option<&mut T> { if Rc::is_unique(this) { unsafe { Some(&mut this.ptr.as_mut().value) } } else { None } } #[inline] #[stable(feature = "ptr_eq", since = "1.17.0")] /// Returns `true` if the two `Rc`s point to the same value (not /// just values that compare as equal). /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let five = Rc::new(5); /// let same_five = Rc::clone(&five); /// let other_five = Rc::new(5); /// /// assert!(Rc::ptr_eq(&five, &same_five)); /// assert!(!Rc::ptr_eq(&five, &other_five)); /// ``` pub fn ptr_eq(this: &Self, other: &Self) -> bool { this.ptr.as_ptr() == other.ptr.as_ptr() } } impl<T: Clone> Rc<T> { /// Makes a mutable reference into the given `Rc`. /// /// If there are other `Rc` or [`Weak`][weak] pointers to the same value, /// then `make_mut` will invoke [`clone`][clone] on the inner value to /// ensure unique ownership. This is also referred to as clone-on-write. /// /// See also [`get_mut`][get_mut], which will fail rather than cloning. /// /// [weak]: struct.Weak.html /// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone /// [get_mut]: struct.Rc.html#method.get_mut /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let mut data = Rc::new(5); /// /// *Rc::make_mut(&mut data) += 1; // Won't clone anything /// let mut other_data = Rc::clone(&data); // Won't clone inner data /// *Rc::make_mut(&mut data) += 1; // Clones inner data /// *Rc::make_mut(&mut data) += 1; // Won't clone anything /// *Rc::make_mut(&mut other_data) *= 2; // Won't clone anything /// /// // Now `data` and `other_data` point to different values. /// assert_eq!(*data, 8); /// assert_eq!(*other_data, 12); /// ``` #[inline] #[stable(feature = "rc_unique", since = "1.4.0")] pub fn make_mut(this: &mut Self) -> &mut T { if Rc::strong_count(this) != 1 { // Gotta clone the data, there are other Rcs *this = Rc::new((**this).clone()) } else if Rc::weak_count(this) != 0 { // Can just steal the data, all that's left is Weaks unsafe { let mut swap = Rc::new(ptr::read(&this.ptr.as_ref().value)); mem::swap(this, &mut swap); swap.dec_strong(); // Remove implicit strong-weak ref (no need to craft a fake // Weak here -- we know other Weaks can clean up for us) swap.dec_weak(); forget(swap); } } // This unsafety is ok because we're guaranteed that the pointer // returned is the *only* pointer that will ever be returned to T. Our // reference count is guaranteed to be 1 at this point, and we required // the `Rc<T>` itself to be `mut`, so we're returning the only possible // reference to the inner value. unsafe { &mut this.ptr.as_mut().value } } } impl Rc<dyn Any> { #[inline] #[stable(feature = "rc_downcast", since = "1.29.0")] /// Attempt to downcast the `Rc<dyn Any>` to a concrete type. /// /// # Examples /// /// ``` /// use std::any::Any; /// use std::rc::Rc; /// /// fn print_if_string(value: Rc<dyn Any>) { /// if let Ok(string) = value.downcast::<String>() { /// println!("String ({}): {}", string.len(), string); /// } /// } /// /// fn main() { /// let my_string = "Hello World".to_string(); /// print_if_string(Rc::new(my_string)); /// print_if_string(Rc::new(0i8)); /// } /// ``` pub fn downcast<T: Any>(self) -> Result<Rc<T>, Rc<dyn Any>> { if (*self).is::<T>() { let ptr = self.ptr.cast::<RcBox<T>>(); forget(self); Ok(Rc { ptr, phantom: PhantomData }) } else { Err(self) } } } impl<T: ?Sized> Rc<T> { // Allocates an `RcBox<T>` with sufficient space for an unsized value unsafe fn allocate_for_ptr(ptr: *const T) -> *mut RcBox<T> { // Calculate layout using the given value. // Previously, layout was calculated on the expression // `&*(ptr as *const RcBox<T>)`, but this created a misaligned // reference (see #54908). let layout = Layout::new::<RcBox<()>>() .extend(Layout::for_value(&*ptr)).unwrap().0 .pad_to_align().unwrap(); let mem = Global.alloc(layout) .unwrap_or_else(|_| handle_alloc_error(layout)); // Initialize the RcBox let inner = set_data_ptr(ptr as *mut T, mem.as_ptr() as *mut u8) as *mut RcBox<T>; debug_assert_eq!(Layout::for_value(&*inner), layout); ptr::write(&mut (*inner).strong, Cell::new(1)); ptr::write(&mut (*inner).weak, Cell::new(1)); inner } fn from_box(v: Box<T>) -> Rc<T> { unsafe { let box_unique = Box::into_unique(v); let bptr = box_unique.as_ptr(); let value_size = size_of_val(&*bptr); let ptr = Self::allocate_for_ptr(bptr); // Copy value as bytes ptr::copy_nonoverlapping( bptr as *const T as *const u8, &mut (*ptr).value as *mut _ as *mut u8, value_size); // Free the allocation without dropping its contents box_free(box_unique); Rc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData } } } } // Sets the data pointer of a `?Sized` raw pointer. // // For a slice/trait object, this sets the `data` field and leaves the rest // unchanged. For a sized raw pointer, this simply sets the pointer. unsafe fn set_data_ptr<T: ?Sized, U>(mut ptr: *mut T, data: *mut U) -> *mut T { ptr::write(&mut ptr as *mut _ as *mut *mut u8, data as *mut u8); ptr } impl<T> Rc<[T]> { // Copy elements from slice into newly allocated Rc<[T]> // // Unsafe because the caller must either take ownership or bind `T: Copy` unsafe fn copy_from_slice(v: &[T]) -> Rc<[T]> { let v_ptr = v as *const [T]; let ptr = Self::allocate_for_ptr(v_ptr); ptr::copy_nonoverlapping( v.as_ptr(), &mut (*ptr).value as *mut [T] as *mut T, v.len()); Rc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData } } } trait RcFromSlice<T> { fn from_slice(slice: &[T]) -> Self; } impl<T: Clone> RcFromSlice<T> for Rc<[T]> { #[inline] default fn from_slice(v: &[T]) -> Self { // Panic guard while cloning T elements. // In the event of a panic, elements that have been written // into the new RcBox will be dropped, then the memory freed. struct Guard<T> { mem: NonNull<u8>, elems: *mut T, layout: Layout, n_elems: usize, } impl<T> Drop for Guard<T> { fn drop(&mut self) { unsafe { let slice = from_raw_parts_mut(self.elems, self.n_elems); ptr::drop_in_place(slice); Global.dealloc(self.mem, self.layout.clone()); } } } unsafe { let v_ptr = v as *const [T]; let ptr = Self::allocate_for_ptr(v_ptr); let mem = ptr as *mut _ as *mut u8; let layout = Layout::for_value(&*ptr); // Pointer to first element let elems = &mut (*ptr).value as *mut [T] as *mut T; let mut guard = Guard{ mem: NonNull::new_unchecked(mem), elems: elems, layout: layout, n_elems: 0, }; for (i, item) in v.iter().enumerate() { ptr::write(elems.add(i), item.clone()); guard.n_elems += 1; } // All clear. Forget the guard so it doesn't free the new RcBox. forget(guard); Rc { ptr: NonNull::new_unchecked(ptr), phantom: PhantomData } } } } impl<T: Copy> RcFromSlice<T> for Rc<[T]> { #[inline] fn from_slice(v: &[T]) -> Self { unsafe { Rc::copy_from_slice(v) } } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized> Deref for Rc<T> { type Target = T; #[inline(always)] fn deref(&self) -> &T { &self.inner().value } } #[unstable(feature = "receiver_trait", issue = "0")] impl<T: ?Sized> Receiver for Rc<T> {} #[stable(feature = "rust1", since = "1.0.0")] unsafe impl<#[may_dangle] T: ?Sized> Drop for Rc<T> { /// Drops the `Rc`. /// /// This will decrement the strong reference count. If the strong reference /// count reaches zero then the only other references (if any) are /// [`Weak`], so we `drop` the inner value. /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// struct Foo; /// /// impl Drop for Foo { /// fn drop(&mut self) { /// println!("dropped!"); /// } /// } /// /// let foo = Rc::new(Foo); /// let foo2 = Rc::clone(&foo); /// /// drop(foo); // Doesn't print anything /// drop(foo2); // Prints "dropped!" /// ``` /// /// [`Weak`]: ../../std/rc/struct.Weak.html fn drop(&mut self) { unsafe { self.dec_strong(); if self.strong() == 0 { // destroy the contained object ptr::drop_in_place(self.ptr.as_mut()); // remove the implicit "strong weak" pointer now that we've // destroyed the contents. self.dec_weak(); if self.weak() == 0 { Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref())); } } } } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized> Clone for Rc<T> { /// Makes a clone of the `Rc` pointer. /// /// This creates another pointer to the same inner value, increasing the /// strong reference count. /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let five = Rc::new(5); /// /// let _ = Rc::clone(&five); /// ``` #[inline] fn clone(&self) -> Rc<T> { self.inc_strong(); Rc { ptr: self.ptr, phantom: PhantomData } } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: Default> Default for Rc<T> { /// Creates a new `Rc<T>`, with the `Default` value for `T`. /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let x: Rc<i32> = Default::default(); /// assert_eq!(*x, 0); /// ``` #[inline] fn default() -> Rc<T> { Rc::new(Default::default()) } } #[stable(feature = "rust1", since = "1.0.0")] trait RcEqIdent<T: ?Sized + PartialEq> { fn eq(&self, other: &Rc<T>) -> bool; fn ne(&self, other: &Rc<T>) -> bool; } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized + PartialEq> RcEqIdent<T> for Rc<T> { #[inline] default fn eq(&self, other: &Rc<T>) -> bool { **self == **other } #[inline] default fn ne(&self, other: &Rc<T>) -> bool { **self != **other } } /// We're doing this specialization here, and not as a more general optimization on `&T`, because it /// would otherwise add a cost to all equality checks on refs. We assume that `Rc`s are used to /// store large values, that are slow to clone, but also heavy to check for equality, causing this /// cost to pay off more easily. It's also more likely to have two `Rc` clones, that point to /// the same value, than two `&T`s. #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized + Eq> RcEqIdent<T> for Rc<T> { #[inline] fn eq(&self, other: &Rc<T>) -> bool { Rc::ptr_eq(self, other) || **self == **other } #[inline] fn ne(&self, other: &Rc<T>) -> bool { !Rc::ptr_eq(self, other) && **self != **other } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized + PartialEq> PartialEq for Rc<T> { /// Equality for two `Rc`s. /// /// Two `Rc`s are equal if their inner values are equal. /// /// If `T` also implements `Eq`, two `Rc`s that point to the same value are /// always equal. /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let five = Rc::new(5); /// /// assert!(five == Rc::new(5)); /// ``` #[inline] fn eq(&self, other: &Rc<T>) -> bool { RcEqIdent::eq(self, other) } /// Inequality for two `Rc`s. /// /// Two `Rc`s are unequal if their inner values are unequal. /// /// If `T` also implements `Eq`, two `Rc`s that point to the same value are /// never unequal. /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let five = Rc::new(5); /// /// assert!(five != Rc::new(6)); /// ``` #[inline] fn ne(&self, other: &Rc<T>) -> bool { RcEqIdent::ne(self, other) } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized + Eq> Eq for Rc<T> {} #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized + PartialOrd> PartialOrd for Rc<T> { /// Partial comparison for two `Rc`s. /// /// The two are compared by calling `partial_cmp()` on their inner values. /// /// # Examples /// /// ``` /// use std::rc::Rc; /// use std::cmp::Ordering; /// /// let five = Rc::new(5); /// /// assert_eq!(Some(Ordering::Less), five.partial_cmp(&Rc::new(6))); /// ``` #[inline(always)] fn partial_cmp(&self, other: &Rc<T>) -> Option<Ordering> { (**self).partial_cmp(&**other) } /// Less-than comparison for two `Rc`s. /// /// The two are compared by calling `<` on their inner values. /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let five = Rc::new(5); /// /// assert!(five < Rc::new(6)); /// ``` #[inline(always)] fn lt(&self, other: &Rc<T>) -> bool { **self < **other } /// 'Less than or equal to' comparison for two `Rc`s. /// /// The two are compared by calling `<=` on their inner values. /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let five = Rc::new(5); /// /// assert!(five <= Rc::new(5)); /// ``` #[inline(always)] fn le(&self, other: &Rc<T>) -> bool { **self <= **other } /// Greater-than comparison for two `Rc`s. /// /// The two are compared by calling `>` on their inner values. /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let five = Rc::new(5); /// /// assert!(five > Rc::new(4)); /// ``` #[inline(always)] fn gt(&self, other: &Rc<T>) -> bool { **self > **other } /// 'Greater than or equal to' comparison for two `Rc`s. /// /// The two are compared by calling `>=` on their inner values. /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let five = Rc::new(5); /// /// assert!(five >= Rc::new(5)); /// ``` #[inline(always)] fn ge(&self, other: &Rc<T>) -> bool { **self >= **other } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized + Ord> Ord for Rc<T> { /// Comparison for two `Rc`s. /// /// The two are compared by calling `cmp()` on their inner values. /// /// # Examples /// /// ``` /// use std::rc::Rc; /// use std::cmp::Ordering; /// /// let five = Rc::new(5); /// /// assert_eq!(Ordering::Less, five.cmp(&Rc::new(6))); /// ``` #[inline] fn cmp(&self, other: &Rc<T>) -> Ordering { (**self).cmp(&**other) } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized + Hash> Hash for Rc<T> { fn hash<H: Hasher>(&self, state: &mut H) { (**self).hash(state); } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized + fmt::Display> fmt::Display for Rc<T> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { fmt::Display::fmt(&**self, f) } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized + fmt::Debug> fmt::Debug for Rc<T> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { fmt::Debug::fmt(&**self, f) } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized> fmt::Pointer for Rc<T> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { fmt::Pointer::fmt(&(&**self as *const T), f) } } #[stable(feature = "from_for_ptrs", since = "1.6.0")] impl<T> From<T> for Rc<T> { fn from(t: T) -> Self { Rc::new(t) } } #[stable(feature = "shared_from_slice", since = "1.21.0")] impl<T: Clone> From<&[T]> for Rc<[T]> { #[inline] fn from(v: &[T]) -> Rc<[T]> { <Self as RcFromSlice<T>>::from_slice(v) } } #[stable(feature = "shared_from_slice", since = "1.21.0")] impl From<&str> for Rc<str> { #[inline] fn from(v: &str) -> Rc<str> { let rc = Rc::<[u8]>::from(v.as_bytes()); unsafe { Rc::from_raw(Rc::into_raw(rc) as *const str) } } } #[stable(feature = "shared_from_slice", since = "1.21.0")] impl From<String> for Rc<str> { #[inline] fn from(v: String) -> Rc<str> { Rc::from(&v[..]) } } #[stable(feature = "shared_from_slice", since = "1.21.0")] impl<T: ?Sized> From<Box<T>> for Rc<T> { #[inline] fn from(v: Box<T>) -> Rc<T> { Rc::from_box(v) } } #[stable(feature = "shared_from_slice", since = "1.21.0")] impl<T> From<Vec<T>> for Rc<[T]> { #[inline] fn from(mut v: Vec<T>) -> Rc<[T]> { unsafe { let rc = Rc::copy_from_slice(&v); // Allow the Vec to free its memory, but not destroy its contents v.set_len(0); rc } } } /// `Weak` is a version of [`Rc`] that holds a non-owning reference to the /// managed value. The value is accessed by calling [`upgrade`] on the `Weak` /// pointer, which returns an [`Option`]`<`[`Rc`]`<T>>`. /// /// Since a `Weak` reference does not count towards ownership, it will not /// prevent the inner value from being dropped, and `Weak` itself makes no /// guarantees about the value still being present and may return [`None`] /// when [`upgrade`]d. /// /// A `Weak` pointer is useful for keeping a temporary reference to the value /// within [`Rc`] without extending its lifetime. It is also used to prevent /// circular references between [`Rc`] pointers, since mutual owning references /// would never allow either [`Rc`] to be dropped. For example, a tree could /// have strong [`Rc`] pointers from parent nodes to children, and `Weak` /// pointers from children back to their parents. /// /// The typical way to obtain a `Weak` pointer is to call [`Rc::downgrade`]. /// /// [`Rc`]: struct.Rc.html /// [`Rc::downgrade`]: struct.Rc.html#method.downgrade /// [`upgrade`]: struct.Weak.html#method.upgrade /// [`Option`]: ../../std/option/enum.Option.html /// [`None`]: ../../std/option/enum.Option.html#variant.None #[stable(feature = "rc_weak", since = "1.4.0")] pub struct Weak<T: ?Sized> { // This is a `NonNull` to allow optimizing the size of this type in enums, // but it is not necessarily a valid pointer. // `Weak::new` sets this to `usize::MAX` so that it doesn’t need // to allocate space on the heap. That's not a value a real pointer // will ever have because RcBox has alignment at least 2. ptr: NonNull<RcBox<T>>, } #[stable(feature = "rc_weak", since = "1.4.0")] impl<T: ?Sized> !marker::Send for Weak<T> {} #[stable(feature = "rc_weak", since = "1.4.0")] impl<T: ?Sized> !marker::Sync for Weak<T> {} #[unstable(feature = "coerce_unsized", issue = "27732")] impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {} #[unstable(feature = "dispatch_from_dyn", issue = "0")] impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Weak<U>> for Weak<T> {} impl<T> Weak<T> { /// Constructs a new `Weak<T>`, without allocating any memory. /// Calling [`upgrade`] on the return value always gives [`None`]. /// /// [`upgrade`]: #method.upgrade /// [`None`]: ../../std/option/enum.Option.html /// /// # Examples /// /// ``` /// use std::rc::Weak; /// /// let empty: Weak<i64> = Weak::new(); /// assert!(empty.upgrade().is_none()); /// ``` #[stable(feature = "downgraded_weak", since = "1.10.0")] pub fn new() -> Weak<T> { Weak { ptr: NonNull::new(usize::MAX as *mut RcBox<T>).expect("MAX is not 0"), } } /// Returns a raw pointer to the object `T` pointed to by this `Weak<T>`. /// /// It is up to the caller to ensure that the object is still alive when accessing it through /// the pointer. /// /// The pointer may be [`null`] or be dangling in case the object has already been destroyed. /// /// # Examples /// /// ``` /// #![feature(weak_into_raw)] /// /// use std::rc::{Rc, Weak}; /// use std::ptr; /// /// let strong = Rc::new(42); /// let weak = Rc::downgrade(&strong); /// // Both point to the same object /// assert!(ptr::eq(&*strong, Weak::as_raw(&weak))); /// // The strong here keeps it alive, so we can still access the object. /// assert_eq!(42, unsafe { *Weak::as_raw(&weak) }); /// /// drop(strong); /// // But not any more. We can do Weak::as_raw(&weak), but accessing the pointer would lead to /// // undefined behaviour. /// // assert_eq!(42, unsafe { *Weak::as_raw(&weak) }); /// ``` /// /// [`null`]: ../../std/ptr/fn.null.html #[unstable(feature = "weak_into_raw", issue = "60728")] pub fn as_raw(this: &Self) -> *const T { match this.inner() { None => ptr::null(), Some(inner) => { let offset = data_offset_sized::<T>(); let ptr = inner as *const RcBox<T>; // Note: while the pointer we create may already point to dropped value, the // allocation still lives (it must hold the weak point as long as we are alive). // Therefore, the offset is OK to do, it won't get out of the allocation. let ptr = unsafe { (ptr as *const u8).offset(offset) }; ptr as *const T } } } /// Consumes the `Weak<T>` and turns it into a raw pointer. /// /// This converts the weak pointer into a raw pointer, preserving the original weak count. It /// can be turned back into the `Weak<T>` with [`from_raw`]. /// /// The same restrictions of accessing the target of the pointer as with /// [`as_raw`] apply. /// /// # Examples /// /// ``` /// #![feature(weak_into_raw)] /// /// use std::rc::{Rc, Weak}; /// /// let strong = Rc::new(42); /// let weak = Rc::downgrade(&strong); /// let raw = Weak::into_raw(weak); /// /// assert_eq!(1, Rc::weak_count(&strong)); /// assert_eq!(42, unsafe { *raw }); /// /// drop(unsafe { Weak::from_raw(raw) }); /// assert_eq!(0, Rc::weak_count(&strong)); /// ``` /// /// [`from_raw`]: struct.Weak.html#method.from_raw /// [`as_raw`]: struct.Weak.html#method.as_raw #[unstable(feature = "weak_into_raw", issue = "60728")] pub fn into_raw(this: Self) -> *const T { let result = Self::as_raw(&this); mem::forget(this); result } /// Converts a raw pointer previously created by [`into_raw`] back into `Weak<T>`. /// /// This can be used to safely get a strong reference (by calling [`upgrade`] /// later) or to deallocate the weak count by dropping the `Weak<T>`. /// /// It takes ownership of one weak count. In case a [`null`] is passed, a dangling [`Weak`] is /// returned. /// /// # Safety /// /// The pointer must represent one valid weak count. In other words, it must point to `T` which /// is or *was* managed by an [`Rc`] and the weak count of that [`Rc`] must not have reached /// 0. It is allowed for the strong count to be 0. /// /// # Examples /// /// ``` /// #![feature(weak_into_raw)] /// /// use std::rc::{Rc, Weak}; /// /// let strong = Rc::new(42); /// /// let raw_1 = Weak::into_raw(Rc::downgrade(&strong)); /// let raw_2 = Weak::into_raw(Rc::downgrade(&strong)); /// /// assert_eq!(2, Rc::weak_count(&strong)); /// /// assert_eq!(42, *Weak::upgrade(&unsafe { Weak::from_raw(raw_1) }).unwrap()); /// assert_eq!(1, Rc::weak_count(&strong)); /// /// drop(strong); /// /// // Decrement the last weak count. /// assert!(Weak::upgrade(&unsafe { Weak::from_raw(raw_2) }).is_none()); /// ``` /// /// [`null`]: ../../std/ptr/fn.null.html /// [`into_raw`]: struct.Weak.html#method.into_raw /// [`upgrade`]: struct.Weak.html#method.upgrade /// [`Rc`]: struct.Rc.html /// [`Weak`]: struct.Weak.html #[unstable(feature = "weak_into_raw", issue = "60728")] pub unsafe fn from_raw(ptr: *const T) -> Self { if ptr.is_null() { Self::new() } else { // See Rc::from_raw for details let offset = data_offset(ptr); let fake_ptr = ptr as *mut RcBox<T>; let ptr = set_data_ptr(fake_ptr, (ptr as *mut u8).offset(-offset)); Weak { ptr: NonNull::new(ptr).expect("Invalid pointer passed to from_raw"), } } } } pub(crate) fn is_dangling<T: ?Sized>(ptr: NonNull<T>) -> bool { let address = ptr.as_ptr() as *mut () as usize; address == usize::MAX } impl<T: ?Sized> Weak<T> { /// Attempts to upgrade the `Weak` pointer to an [`Rc`], extending /// the lifetime of the value if successful. /// /// Returns [`None`] if the value has since been dropped. /// /// [`Rc`]: struct.Rc.html /// [`None`]: ../../std/option/enum.Option.html /// /// # Examples /// /// ``` /// use std::rc::Rc; /// /// let five = Rc::new(5); /// /// let weak_five = Rc::downgrade(&five); /// /// let strong_five: Option<Rc<_>> = weak_five.upgrade(); /// assert!(strong_five.is_some()); /// /// // Destroy all strong pointers. /// drop(strong_five); /// drop(five); /// /// assert!(weak_five.upgrade().is_none()); /// ``` #[stable(feature = "rc_weak", since = "1.4.0")] pub fn upgrade(&self) -> Option<Rc<T>> { let inner = self.inner()?; if inner.strong() == 0 { None } else { inner.inc_strong(); Some(Rc { ptr: self.ptr, phantom: PhantomData }) } } /// Gets the number of strong (`Rc`) pointers pointing to this value. /// /// If `self` was created using [`Weak::new`], this will return 0. /// /// [`Weak::new`]: #method.new #[unstable(feature = "weak_counts", issue = "57977")] pub fn strong_count(&self) -> usize { if let Some(inner) = self.inner() { inner.strong() } else { 0 } } /// Gets the number of `Weak` pointers pointing to this value. /// /// If `self` was created using [`Weak::new`], this will return `None`. If /// not, the returned value is at least 1, since `self` still points to the /// value. /// /// [`Weak::new`]: #method.new #[unstable(feature = "weak_counts", issue = "57977")] pub fn weak_count(&self) -> Option<usize> { self.inner().map(|inner| { if inner.strong() > 0 { inner.weak() - 1 // subtract the implicit weak ptr } else { inner.weak() } }) } /// Returns `None` when the pointer is dangling and there is no allocated `RcBox` /// (i.e., when this `Weak` was created by `Weak::new`). #[inline] fn inner(&self) -> Option<&RcBox<T>> { if is_dangling(self.ptr) { None } else { Some(unsafe { self.ptr.as_ref() }) } } /// Returns `true` if the two `Weak`s point to the same value (not just values /// that compare as equal). /// /// # Notes /// /// Since this compares pointers it means that `Weak::new()` will equal each /// other, even though they don't point to any value. /// /// # Examples /// /// ``` /// #![feature(weak_ptr_eq)] /// use std::rc::{Rc, Weak}; /// /// let first_rc = Rc::new(5); /// let first = Rc::downgrade(&first_rc); /// let second = Rc::downgrade(&first_rc); /// /// assert!(Weak::ptr_eq(&first, &second)); /// /// let third_rc = Rc::new(5); /// let third = Rc::downgrade(&third_rc); /// /// assert!(!Weak::ptr_eq(&first, &third)); /// ``` /// /// Comparing `Weak::new`. /// /// ``` /// #![feature(weak_ptr_eq)] /// use std::rc::{Rc, Weak}; /// /// let first = Weak::new(); /// let second = Weak::new(); /// assert!(Weak::ptr_eq(&first, &second)); /// /// let third_rc = Rc::new(()); /// let third = Rc::downgrade(&third_rc); /// assert!(!Weak::ptr_eq(&first, &third)); /// ``` #[inline] #[unstable(feature = "weak_ptr_eq", issue = "55981")] pub fn ptr_eq(this: &Self, other: &Self) -> bool { this.ptr.as_ptr() == other.ptr.as_ptr() } } #[stable(feature = "rc_weak", since = "1.4.0")] impl<T: ?Sized> Drop for Weak<T> { /// Drops the `Weak` pointer. /// /// # Examples /// /// ``` /// use std::rc::{Rc, Weak}; /// /// struct Foo; /// /// impl Drop for Foo { /// fn drop(&mut self) { /// println!("dropped!"); /// } /// } /// /// let foo = Rc::new(Foo); /// let weak_foo = Rc::downgrade(&foo); /// let other_weak_foo = Weak::clone(&weak_foo); /// /// drop(weak_foo); // Doesn't print anything /// drop(foo); // Prints "dropped!" /// /// assert!(other_weak_foo.upgrade().is_none()); /// ``` fn drop(&mut self) { if let Some(inner) = self.inner() { inner.dec_weak(); // the weak count starts at 1, and will only go to zero if all // the strong pointers have disappeared. if inner.weak() == 0 { unsafe { Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref())); } } } } } #[stable(feature = "rc_weak", since = "1.4.0")] impl<T: ?Sized> Clone for Weak<T> { /// Makes a clone of the `Weak` pointer that points to the same value. /// /// # Examples /// /// ``` /// use std::rc::{Rc, Weak}; /// /// let weak_five = Rc::downgrade(&Rc::new(5)); /// /// let _ = Weak::clone(&weak_five); /// ``` #[inline] fn clone(&self) -> Weak<T> { if let Some(inner) = self.inner() { inner.inc_weak() } Weak { ptr: self.ptr } } } #[stable(feature = "rc_weak", since = "1.4.0")] impl<T: ?Sized + fmt::Debug> fmt::Debug for Weak<T> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { write!(f, "(Weak)") } } #[stable(feature = "downgraded_weak", since = "1.10.0")] impl<T> Default for Weak<T> { /// Constructs a new `Weak<T>`, allocating memory for `T` without initializing /// it. Calling [`upgrade`] on the return value always gives [`None`]. /// /// [`None`]: ../../std/option/enum.Option.html /// [`upgrade`]: ../../std/rc/struct.Weak.html#method.upgrade /// /// # Examples /// /// ``` /// use std::rc::Weak; /// /// let empty: Weak<i64> = Default::default(); /// assert!(empty.upgrade().is_none()); /// ``` fn default() -> Weak<T> { Weak::new() } } // NOTE: We checked_add here to deal with mem::forget safely. In particular // if you mem::forget Rcs (or Weaks), the ref-count can overflow, and then // you can free the allocation while outstanding Rcs (or Weaks) exist. // We abort because this is such a degenerate scenario that we don't care about // what happens -- no real program should ever experience this. // // This should have negligible overhead since you don't actually need to // clone these much in Rust thanks to ownership and move-semantics. #[doc(hidden)] trait RcBoxPtr<T: ?Sized> { fn inner(&self) -> &RcBox<T>; #[inline] fn strong(&self) -> usize { self.inner().strong.get() } #[inline] fn inc_strong(&self) { // We want to abort on overflow instead of dropping the value. // The reference count will never be zero when this is called; // nevertheless, we insert an abort here to hint LLVM at // an otherwise missed optimization. if self.strong() == 0 || self.strong() == usize::max_value() { unsafe { abort(); } } self.inner().strong.set(self.strong() + 1); } #[inline] fn dec_strong(&self) { self.inner().strong.set(self.strong() - 1); } #[inline] fn weak(&self) -> usize { self.inner().weak.get() } #[inline] fn inc_weak(&self) { // We want to abort on overflow instead of dropping the value. // The reference count will never be zero when this is called; // nevertheless, we insert an abort here to hint LLVM at // an otherwise missed optimization. if self.weak() == 0 || self.weak() == usize::max_value() { unsafe { abort(); } } self.inner().weak.set(self.weak() + 1); } #[inline] fn dec_weak(&self) { self.inner().weak.set(self.weak() - 1); } } impl<T: ?Sized> RcBoxPtr<T> for Rc<T> { #[inline(always)] fn inner(&self) -> &RcBox<T> { unsafe { self.ptr.as_ref() } } } impl<T: ?Sized> RcBoxPtr<T> for RcBox<T> { #[inline(always)] fn inner(&self) -> &RcBox<T> { self } } #[cfg(test)] mod tests { use super::{Rc, Weak}; use std::boxed::Box; use std::cell::RefCell; use std::option::Option::{self, None, Some}; use std::result::Result::{Err, Ok}; use std::mem::drop; use std::clone::Clone; use std::convert::From; #[test] fn test_clone() { let x = Rc::new(RefCell::new(5)); let y = x.clone(); *x.borrow_mut() = 20; assert_eq!(*y.borrow(), 20); } #[test] fn test_simple() { let x = Rc::new(5); assert_eq!(*x, 5); } #[test] fn test_simple_clone() { let x = Rc::new(5); let y = x.clone(); assert_eq!(*x, 5); assert_eq!(*y, 5); } #[test] fn test_destructor() { let x: Rc<Box<_>> = Rc::new(box 5); assert_eq!(**x, 5); } #[test] fn test_live() { let x = Rc::new(5); let y = Rc::downgrade(&x); assert!(y.upgrade().is_some()); } #[test] fn test_dead() { let x = Rc::new(5); let y = Rc::downgrade(&x); drop(x); assert!(y.upgrade().is_none()); } #[test] fn weak_self_cyclic() { struct Cycle { x: RefCell<Option<Weak<Cycle>>>, } let a = Rc::new(Cycle { x: RefCell::new(None) }); let b = Rc::downgrade(&a.clone()); *a.x.borrow_mut() = Some(b); // hopefully we don't double-free (or leak)... } #[test] fn is_unique() { let x = Rc::new(3); assert!(Rc::is_unique(&x)); let y = x.clone(); assert!(!Rc::is_unique(&x)); drop(y); assert!(Rc::is_unique(&x)); let w = Rc::downgrade(&x); assert!(!Rc::is_unique(&x)); drop(w); assert!(Rc::is_unique(&x)); } #[test] fn test_strong_count() { let a = Rc::new(0); assert!(Rc::strong_count(&a) == 1); let w = Rc::downgrade(&a); assert!(Rc::strong_count(&a) == 1); let b = w.upgrade().expect("upgrade of live rc failed"); assert!(Rc::strong_count(&b) == 2); assert!(Rc::strong_count(&a) == 2); drop(w); drop(a); assert!(Rc::strong_count(&b) == 1); let c = b.clone(); assert!(Rc::strong_count(&b) == 2); assert!(Rc::strong_count(&c) == 2); } #[test] fn test_weak_count() { let a = Rc::new(0); assert!(Rc::strong_count(&a) == 1); assert!(Rc::weak_count(&a) == 0); let w = Rc::downgrade(&a); assert!(Rc::strong_count(&a) == 1); assert!(Rc::weak_count(&a) == 1); drop(w); assert!(Rc::strong_count(&a) == 1); assert!(Rc::weak_count(&a) == 0); let c = a.clone(); assert!(Rc::strong_count(&a) == 2); assert!(Rc::weak_count(&a) == 0); drop(c); } #[test] fn weak_counts() { assert_eq!(Weak::weak_count(&Weak::<u64>::new()), None); assert_eq!(Weak::strong_count(&Weak::<u64>::new()), 0); let a = Rc::new(0); let w = Rc::downgrade(&a); assert_eq!(Weak::strong_count(&w), 1); assert_eq!(Weak::weak_count(&w), Some(1)); let w2 = w.clone(); assert_eq!(Weak::strong_count(&w), 1); assert_eq!(Weak::weak_count(&w), Some(2)); assert_eq!(Weak::strong_count(&w2), 1); assert_eq!(Weak::weak_count(&w2), Some(2)); drop(w); assert_eq!(Weak::strong_count(&w2), 1); assert_eq!(Weak::weak_count(&w2), Some(1)); let a2 = a.clone(); assert_eq!(Weak::strong_count(&w2), 2); assert_eq!(Weak::weak_count(&w2), Some(1)); drop(a2); drop(a); assert_eq!(Weak::strong_count(&w2), 0); assert_eq!(Weak::weak_count(&w2), Some(1)); drop(w2); } #[test] fn try_unwrap() { let x = Rc::new(3); assert_eq!(Rc::try_unwrap(x), Ok(3)); let x = Rc::new(4); let _y = x.clone(); assert_eq!(Rc::try_unwrap(x), Err(Rc::new(4))); let x = Rc::new(5); let _w = Rc::downgrade(&x); assert_eq!(Rc::try_unwrap(x), Ok(5)); } #[test] fn into_from_raw() { let x = Rc::new(box "hello"); let y = x.clone(); let x_ptr = Rc::into_raw(x); drop(y); unsafe { assert_eq!(**x_ptr, "hello"); let x = Rc::from_raw(x_ptr); assert_eq!(**x, "hello"); assert_eq!(Rc::try_unwrap(x).map(|x| *x), Ok("hello")); } } #[test] fn test_into_from_raw_unsized() { use std::fmt::Display; use std::string::ToString; let rc: Rc<str> = Rc::from("foo"); let ptr = Rc::into_raw(rc.clone()); let rc2 = unsafe { Rc::from_raw(ptr) }; assert_eq!(unsafe { &*ptr }, "foo"); assert_eq!(rc, rc2); let rc: Rc<dyn Display> = Rc::new(123); let ptr = Rc::into_raw(rc.clone()); let rc2 = unsafe { Rc::from_raw(ptr) }; assert_eq!(unsafe { &*ptr }.to_string(), "123"); assert_eq!(rc2.to_string(), "123"); } #[test] fn get_mut() { let mut x = Rc::new(3); *Rc::get_mut(&mut x).unwrap() = 4; assert_eq!(*x, 4); let y = x.clone(); assert!(Rc::get_mut(&mut x).is_none()); drop(y); assert!(Rc::get_mut(&mut x).is_some()); let _w = Rc::downgrade(&x); assert!(Rc::get_mut(&mut x).is_none()); } #[test] fn test_cowrc_clone_make_unique() { let mut cow0 = Rc::new(75); let mut cow1 = cow0.clone(); let mut cow2 = cow1.clone(); assert!(75 == *Rc::make_mut(&mut cow0)); assert!(75 == *Rc::make_mut(&mut cow1)); assert!(75 == *Rc::make_mut(&mut cow2)); *Rc::make_mut(&mut cow0) += 1; *Rc::make_mut(&mut cow1) += 2; *Rc::make_mut(&mut cow2) += 3; assert!(76 == *cow0); assert!(77 == *cow1); assert!(78 == *cow2); // none should point to the same backing memory assert!(*cow0 != *cow1); assert!(*cow0 != *cow2); assert!(*cow1 != *cow2); } #[test] fn test_cowrc_clone_unique2() { let mut cow0 = Rc::new(75); let cow1 = cow0.clone(); let cow2 = cow1.clone(); assert!(75 == *cow0); assert!(75 == *cow1); assert!(75 == *cow2); *Rc::make_mut(&mut cow0) += 1; assert!(76 == *cow0); assert!(75 == *cow1); assert!(75 == *cow2); // cow1 and cow2 should share the same contents // cow0 should have a unique reference assert!(*cow0 != *cow1); assert!(*cow0 != *cow2); assert!(*cow1 == *cow2); } #[test] fn test_cowrc_clone_weak() { let mut cow0 = Rc::new(75); let cow1_weak = Rc::downgrade(&cow0); assert!(75 == *cow0); assert!(75 == *cow1_weak.upgrade().unwrap()); *Rc::make_mut(&mut cow0) += 1; assert!(76 == *cow0); assert!(cow1_weak.upgrade().is_none()); } #[test] fn test_show() { let foo = Rc::new(75); assert_eq!(format!("{:?}", foo), "75"); } #[test] fn test_unsized() { let foo: Rc<[i32]> = Rc::new([1, 2, 3]); assert_eq!(foo, foo.clone()); } #[test] fn test_from_owned() { let foo = 123; let foo_rc = Rc::from(foo); assert!(123 == *foo_rc); } #[test] fn test_new_weak() { let foo: Weak<usize> = Weak::new(); assert!(foo.upgrade().is_none()); } #[test] fn test_ptr_eq() { let five = Rc::new(5); let same_five = five.clone(); let other_five = Rc::new(5); assert!(Rc::ptr_eq(&five, &same_five)); assert!(!Rc::ptr_eq(&five, &other_five)); } #[test] fn test_from_str() { let r: Rc<str> = Rc::from("foo"); assert_eq!(&r[..], "foo"); } #[test] fn test_copy_from_slice() { let s: &[u32] = &[1, 2, 3]; let r: Rc<[u32]> = Rc::from(s); assert_eq!(&r[..], [1, 2, 3]); } #[test] fn test_clone_from_slice() { #[derive(Clone, Debug, Eq, PartialEq)] struct X(u32); let s: &[X] = &[X(1), X(2), X(3)]; let r: Rc<[X]> = Rc::from(s); assert_eq!(&r[..], s); } #[test] #[should_panic] fn test_clone_from_slice_panic() { use std::string::{String, ToString}; struct Fail(u32, String); impl Clone for Fail { fn clone(&self) -> Fail { if self.0 == 2 { panic!(); } Fail(self.0, self.1.clone()) } } let s: &[Fail] = &[ Fail(0, "foo".to_string()), Fail(1, "bar".to_string()), Fail(2, "baz".to_string()), ]; // Should panic, but not cause memory corruption let _r: Rc<[Fail]> = Rc::from(s); } #[test] fn test_from_box() { let b: Box<u32> = box 123; let r: Rc<u32> = Rc::from(b); assert_eq!(*r, 123); } #[test] fn test_from_box_str() { use std::string::String; let s = String::from("foo").into_boxed_str(); let r: Rc<str> = Rc::from(s); assert_eq!(&r[..], "foo"); } #[test] fn test_from_box_slice() { let s = vec![1, 2, 3].into_boxed_slice(); let r: Rc<[u32]> = Rc::from(s); assert_eq!(&r[..], [1, 2, 3]); } #[test] fn test_from_box_trait() { use std::fmt::Display; use std::string::ToString; let b: Box<dyn Display> = box 123; let r: Rc<dyn Display> = Rc::from(b); assert_eq!(r.to_string(), "123"); } #[test] fn test_from_box_trait_zero_sized() { use std::fmt::Debug; let b: Box<dyn Debug> = box (); let r: Rc<dyn Debug> = Rc::from(b); assert_eq!(format!("{:?}", r), "()"); } #[test] fn test_from_vec() { let v = vec![1, 2, 3]; let r: Rc<[u32]> = Rc::from(v); assert_eq!(&r[..], [1, 2, 3]); } #[test] fn test_downcast() { use std::any::Any; let r1: Rc<dyn Any> = Rc::new(i32::max_value()); let r2: Rc<dyn Any> = Rc::new("abc"); assert!(r1.clone().downcast::<u32>().is_err()); let r1i32 = r1.downcast::<i32>(); assert!(r1i32.is_ok()); assert_eq!(r1i32.unwrap(), Rc::new(i32::max_value())); assert!(r2.clone().downcast::<i32>().is_err()); let r2str = r2.downcast::<&'static str>(); assert!(r2str.is_ok()); assert_eq!(r2str.unwrap(), Rc::new("abc")); } } #[stable(feature = "rust1", since = "1.0.0")] impl<T: ?Sized> borrow::Borrow<T> for Rc<T> { fn borrow(&self) -> &T { &**self } } #[stable(since = "1.5.0", feature = "smart_ptr_as_ref")] impl<T: ?Sized> AsRef<T> for Rc<T> { fn as_ref(&self) -> &T { &**self } } #[stable(feature = "pin", since = "1.33.0")] impl<T: ?Sized> Unpin for Rc<T> { } unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize { // Align the unsized value to the end of the RcBox. // Because it is ?Sized, it will always be the last field in memory. let align = align_of_val(&*ptr); let layout = Layout::new::<RcBox<()>>(); (layout.size() + layout.padding_needed_for(align)) as isize } /// Computes the offset of the data field within ArcInner. /// /// Unlike [`data_offset`], this doesn't need the pointer, but it works only on `T: Sized`. fn data_offset_sized<T>() -> isize { let align = align_of::<T>(); let layout = Layout::new::<RcBox<()>>(); (layout.size() + layout.padding_needed_for(align)) as isize }