[rustc.git] / src / doc / trpl / intrinsics.md

% Intrinsics

> **Note**: intrinsics will forever have an unstable interface, it is
> recommended to use the stable interfaces of libcore rather than intrinsics
> directly.

These are imported as if they were FFI functions, with the special
`rust-intrinsic` ABI. For example, if one was in a freestanding
context, but wished to be able to `transmute` between types, and
perform efficient pointer arithmetic, one would import those functions
via a declaration like

```rust
#![feature(intrinsics)]
# fn main() {}

extern "rust-intrinsic" {
    fn transmute<T, U>(x: T) -> U;

    fn offset<T>(dst: *const T, offset: isize) -> *const T;
}
```

As with any other FFI functions, these are always `unsafe` to call.
Commit	Line	Data
c34b1796 AL	1	% Intrinsics
	2
	3	> Note: intrinsics will forever have an unstable interface, it is
	4	> recommended to use the stable interfaces of libcore rather than intrinsics
	5	> directly.
	6
	7	These are imported as if they were FFI functions, with the special
	8	`rust-intrinsic` ABI. For example, if one was in a freestanding
	9	context, but wished to be able to `transmute` between types, and
	10	perform efficient pointer arithmetic, one would import those functions
	11	via a declaration like
	12
62682a34	13	```rust
c1a9b12d	14	#![feature(intrinsics)]
c34b1796 AL	15	# fn main() {}
	16
	17	extern "rust-intrinsic" {
	18	fn transmute<T, U>(x: T) -> U;
	19
	20	fn offset<T>(dst: const T, offset: isize) -> const T;
	21	}
	22	```
	23
	24	As with any other FFI functions, these are always `unsafe` to call.
	25