1.0.0[−][src]Trait core::convert::From
Used to do value-to-value conversions while consuming the input value. It is the reciprocal of
Into
.
One should always prefer implementing From
over Into
because implementing From
automatically provides one with a implementation of Into
thanks to the blanket implementation in the standard library.
Only implement Into
if a conversion to a type outside the current crate is required.
From
cannot do these type of conversions because of Rust's orphaning rules.
See Into
for more details.
Prefer using Into
over using From
when specifying trait bounds on a generic function.
This way, types that directly implement Into
can be used as arguments as well.
The From
is also very useful when performing error handling. When constructing a function
that is capable of failing, the return type will generally be of the form Result<T, E>
.
The From
trait simplifies error handling by allowing a function to return a single error type
that encapsulate multiple error types. See the "Examples" section and the book for more
details.
Note: This trait must not fail. If the conversion can fail, use TryFrom
.
Generic Implementations
From<T> for U
impliesInto
<U> for T
From
is reflexive, which means thatFrom<T> for T
is implemented
Examples
String
implements From<&str>
:
An explicit conversion from a &str
to a String is done as follows:
let string = "hello".to_string(); let other_string = String::from("hello"); assert_eq!(string, other_string);Run
While performing error handling it is often useful to implement From
for your own error type.
By converting underlying error types to our own custom error type that encapsulates the
underlying error type, we can return a single error type without losing information on the
underlying cause. The '?' operator automatically converts the underlying error type to our
custom error type by calling Into<CliError>::into
which is automatically provided when
implementing From
. The compiler then infers which implementation of Into
should be used.
use std::fs; use std::io; use std::num; enum CliError { IoError(io::Error), ParseError(num::ParseIntError), } impl From<io::Error> for CliError { fn from(error: io::Error) -> Self { CliError::IoError(error) } } impl From<num::ParseIntError> for CliError { fn from(error: num::ParseIntError) -> Self { CliError::ParseError(error) } } fn open_and_parse_file(file_name: &str) -> Result<i32, CliError> { let mut contents = fs::read_to_string(&file_name)?; let num: i32 = contents.trim().parse()?; Ok(num) }Run
Required methods
fn from(_: T) -> Self
Performs the conversion.
Implementors
impl From<!> for Infallible
[src]
impl From<!> for TryFromIntError
[src]
fn from(never: !) -> TryFromIntError
[src]
impl From<Infallible> for TryFromSliceError
[src]
fn from(x: Infallible) -> TryFromSliceError
[src]
impl From<Infallible> for TryFromIntError
[src]
fn from(x: Infallible) -> TryFromIntError
[src]
impl From<NonZeroI128> for i128
[src]
fn from(nonzero: NonZeroI128) -> Self
[src]
impl From<NonZeroI16> for i16
[src]
fn from(nonzero: NonZeroI16) -> Self
[src]
impl From<NonZeroI32> for i32
[src]
fn from(nonzero: NonZeroI32) -> Self
[src]
impl From<NonZeroI64> for i64
[src]
fn from(nonzero: NonZeroI64) -> Self
[src]
impl From<NonZeroI8> for i8
[src]
impl From<NonZeroIsize> for isize
[src]
fn from(nonzero: NonZeroIsize) -> Self
[src]
impl From<NonZeroU128> for u128
[src]
fn from(nonzero: NonZeroU128) -> Self
[src]
impl From<NonZeroU16> for u16
[src]
fn from(nonzero: NonZeroU16) -> Self
[src]
impl From<NonZeroU32> for u32
[src]
fn from(nonzero: NonZeroU32) -> Self
[src]
impl From<NonZeroU64> for u64
[src]
fn from(nonzero: NonZeroU64) -> Self
[src]
impl From<NonZeroU8> for u8
[src]
impl From<NonZeroUsize> for usize
[src]
fn from(nonzero: NonZeroUsize) -> Self
[src]
impl From<bool> for AtomicBool
[src]
impl From<bool> for i8
[src]
Converts a bool
to a i8
. The resulting value is 0
for false
and 1
for true
values.
Examples
assert_eq!(i8::from(true), 1); assert_eq!(i8::from(false), 0);Run
impl From<bool> for i16
[src]
Converts a bool
to a i16
. The resulting value is 0
for false
and 1
for true
values.
Examples
assert_eq!(i16::from(true), 1); assert_eq!(i16::from(false), 0);Run
impl From<bool> for i32
[src]
Converts a bool
to a i32
. The resulting value is 0
for false
and 1
for true
values.
Examples
assert_eq!(i32::from(true), 1); assert_eq!(i32::from(false), 0);Run
impl From<bool> for i64
[src]
Converts a bool
to a i64
. The resulting value is 0
for false
and 1
for true
values.
Examples
assert_eq!(i64::from(true), 1); assert_eq!(i64::from(false), 0);Run
impl From<bool> for i128
[src]
Converts a bool
to a i128
. The resulting value is 0
for false
and 1
for true
values.
Examples
assert_eq!(i128::from(true), 1); assert_eq!(i128::from(false), 0);Run
impl From<bool> for isize
[src]
Converts a bool
to a isize
. The resulting value is 0
for false
and 1
for true
values.
Examples
assert_eq!(isize::from(true), 1); assert_eq!(isize::from(false), 0);Run
impl From<bool> for u8
[src]
Converts a bool
to a u8
. The resulting value is 0
for false
and 1
for true
values.
Examples
assert_eq!(u8::from(true), 1); assert_eq!(u8::from(false), 0);Run
impl From<bool> for u16
[src]
Converts a bool
to a u16
. The resulting value is 0
for false
and 1
for true
values.
Examples
assert_eq!(u16::from(true), 1); assert_eq!(u16::from(false), 0);Run
impl From<bool> for u32
[src]
Converts a bool
to a u32
. The resulting value is 0
for false
and 1
for true
values.
Examples
assert_eq!(u32::from(true), 1); assert_eq!(u32::from(false), 0);Run
impl From<bool> for u64
[src]
Converts a bool
to a u64
. The resulting value is 0
for false
and 1
for true
values.
Examples
assert_eq!(u64::from(true), 1); assert_eq!(u64::from(false), 0);Run
impl From<bool> for u128
[src]
Converts a bool
to a u128
. The resulting value is 0
for false
and 1
for true
values.
Examples
assert_eq!(u128::from(true), 1); assert_eq!(u128::from(false), 0);Run
impl From<bool> for usize
[src]
Converts a bool
to a usize
. The resulting value is 0
for false
and 1
for true
values.
Examples
assert_eq!(usize::from(true), 1); assert_eq!(usize::from(false), 0);Run
impl From<char> for u32
[src]
impl From<f32> for f64
[src]
Converts f32
to f64
losslessly.
impl From<i8> for isize
[src]
Converts i8
to isize
losslessly.
impl From<i16> for isize
[src]
Converts i16
to isize
losslessly.
impl From<i128> for AtomicI128
[src]
impl From<i16> for AtomicI16
[src]
impl From<i16> for f32
[src]
Converts i16
to f32
losslessly.
impl From<i16> for f64
[src]
Converts i16
to f64
losslessly.
impl From<i16> for i32
[src]
Converts i16
to i32
losslessly.
impl From<i16> for i64
[src]
Converts i16
to i64
losslessly.
impl From<i16> for i128
[src]
Converts i16
to i128
losslessly.
impl From<i32> for AtomicI32
[src]
impl From<i32> for f64
[src]
Converts i32
to f64
losslessly.
impl From<i32> for i64
[src]
Converts i32
to i64
losslessly.
impl From<i32> for i128
[src]
Converts i32
to i128
losslessly.
impl From<i64> for AtomicI64
[src]
impl From<i64> for i128
[src]
Converts i64
to i128
losslessly.
impl From<i8> for AtomicI8
[src]
impl From<i8> for f32
[src]
Converts i8
to f32
losslessly.
impl From<i8> for f64
[src]
Converts i8
to f64
losslessly.
impl From<i8> for i16
[src]
Converts i8
to i16
losslessly.
impl From<i8> for i32
[src]
Converts i8
to i32
losslessly.
impl From<i8> for i64
[src]
Converts i8
to i64
losslessly.
impl From<i8> for i128
[src]
Converts i8
to i128
losslessly.
impl From<isize> for AtomicIsize
[src]
impl From<u8> for usize
[src]
Converts u8
to usize
losslessly.
impl From<u8> for isize
[src]
Converts u8
to isize
losslessly.
impl From<u8> for char
[src]
Maps a byte in 0x00...0xFF to a char
whose code point has the same value, in U+0000 to U+00FF.
Unicode is designed such that this effectively decodes bytes with the character encoding that IANA calls ISO-8859-1. This encoding is compatible with ASCII.
Note that this is different from ISO/IEC 8859-1 a.k.a. ISO 8859-1 (with one less hyphen), which leaves some "blanks", byte values that are not assigned to any character. ISO-8859-1 (the IANA one) assigns them to the C0 and C1 control codes.
Note that this is also different from Windows-1252 a.k.a. code page 1252, which is a superset ISO/IEC 8859-1 that assigns some (not all!) blanks to punctuation and various Latin characters.
To confuse things further, on the Web
ascii
, iso-8859-1
, and windows-1252
are all aliases
for a superset of Windows-1252 that fills the remaining blanks with corresponding
C0 and C1 control codes.
impl From<u16> for usize
[src]
Converts u16
to usize
losslessly.
impl From<u128> for AtomicU128
[src]
impl From<u16> for AtomicU16
[src]
impl From<u16> for f32
[src]
Converts u16
to f32
losslessly.
impl From<u16> for f64
[src]
Converts u16
to f64
losslessly.
impl From<u16> for i32
[src]
Converts u16
to i32
losslessly.
impl From<u16> for i64
[src]
Converts u16
to i64
losslessly.
impl From<u16> for i128
[src]
Converts u16
to i128
losslessly.
impl From<u16> for u32
[src]
Converts u16
to u32
losslessly.
impl From<u16> for u64
[src]
Converts u16
to u64
losslessly.
impl From<u16> for u128
[src]
Converts u16
to u128
losslessly.
impl From<u32> for AtomicU32
[src]
impl From<u32> for f64
[src]
Converts u32
to f64
losslessly.
impl From<u32> for i64
[src]
Converts u32
to i64
losslessly.
impl From<u32> for i128
[src]
Converts u32
to i128
losslessly.
impl From<u32> for u64
[src]
Converts u32
to u64
losslessly.
impl From<u32> for u128
[src]
Converts u32
to u128
losslessly.
impl From<u64> for AtomicU64
[src]
impl From<u64> for i128
[src]
Converts u64
to i128
losslessly.
impl From<u64> for u128
[src]
Converts u64
to u128
losslessly.
impl From<u8> for AtomicU8
[src]
impl From<u8> for f32
[src]
Converts u8
to f32
losslessly.
impl From<u8> for f64
[src]
Converts u8
to f64
losslessly.
impl From<u8> for i16
[src]
Converts u8
to i16
losslessly.
impl From<u8> for i32
[src]
Converts u8
to i32
losslessly.
impl From<u8> for i64
[src]
Converts u8
to i64
losslessly.
impl From<u8> for i128
[src]
Converts u8
to i128
losslessly.
impl From<u8> for u16
[src]
Converts u8
to u16
losslessly.
impl From<u8> for u32
[src]
Converts u8
to u32
losslessly.
impl From<u8> for u64
[src]
Converts u8
to u64
losslessly.
impl From<u8> for u128
[src]
Converts u8
to u128
losslessly.