Function core::mem::forget

pub fn forget<T>(t: T)

Takes ownership and "forgets" about the value without running its destructor.

Any resources the value manages, such as heap memory or a file handle, will linger forever in an unreachable state. However, it does not guarantee that pointers to this memory will remain valid.

• If you want to leak memory, see Box::leak.
• If you want to obtain a raw pointer to the memory, see Box::into_raw.
• If you want to dispose of a value properly, running its destructor, see mem::drop.

Safety

forget is not marked as unsafe, because Rust's safety guarantees do not include a guarantee that destructors will always run. For example, a program can create a reference cycle using Rc, or call process::exit to exit without running destructors. Thus, allowing mem::forget from safe code does not fundamentally change Rust's safety guarantees.

That said, leaking resources such as memory or I/O objects is usually undesirable, so forget is only recommended for specialized use cases like those shown below.

Because forgetting a value is allowed, any unsafe code you write must allow for this possibility. You cannot return a value and expect that the caller will necessarily run the value's destructor.

Examples

Leak an I/O object, never closing the file:

use std::mem;
use std::fs::File;

let file = File::open("foo.txt").unwrap();
mem::forget(file);

The practical use cases for forget are rather specialized and mainly come up in unsafe or FFI code.