as
does a huge number of things. Probably too many. Here's a comprehensive list of everything it can do.
Note that as
conversions are transitive: If a as B as C
compiles, then so does a as C
, though it might not take the same "path" through intermediate conversions.
- int <-> int
zero_extend
: unsigned int -> bigger unsigned int. Pads the number with leading zeroes.sign_extend
: signed int -> bigger signed int. Pads the number with leading zeroes if positive, and leading ones if negative.truncate
: bigger int -> smaller int (regardless of signedness). Throws away the high bits of the numberreinterpret_sign
: int -> int of the same size and opposite signedness. Does nothing to the bits.
- int <-> float
cast_saturate_to_infinity
: Yields the float closest to the specified integer. Yields infinity if the integer is out of bounds.cast_nan_to_zero_saturating_when_out_of_bounds
: Truncates the float and yields the corresponding integer. NaN yields 0, and the infinities yield the minimum and maximum integer value.
- int <-> ptr
expose_addr
: ptr -> int. Does nothing to the bits, and exposes the address (which is a provenance-related concept)from_exposed_addr
: int -> ptr. Does nothing to the bits, inheriting the provenance of a pointer with the same address that was previously exposed.
- ptr <-> ptr
cast
: ptr -> ptr: Does nothing to the bits, keeps the pointer's mutability while changing the typecast_const
->*const T -> *mut T
. Does nothing to the bits. Changes the pointer's mutability while keeping the typecast_mut
->*mut T -> *const T
. Does nothing to the bits. Changes the pointer's mutability while keeping the type
- ptr <-> function pointer
to_fn_ptr
: ptr -> fnptr. Does nothing to the bits.to_data_ptr
: fnptr -> ptr. Does nothing to the bits.
- char -> u32 (this conversion only goes one way)
from
: char -> u32. Does nothing to the bits.
- bool -> u8 (this conversion only goes one way)
from
: bool -> u8 Does nothing to the bits, yields 1 for true and 0 for false.
- ref -> ptr (these conversions only go one way)
as_mut_ptr
:&mut T -> *mut T
. Does nothing to the bits.as_const_ptr
&T -> *const T
. Does nothing to the bits.
- ptr to sized -> ptr to unsized (that is, any pointer or reference, including
Box
,Arc
, etc, fromPtr<T>
toPtr<U>
whereU
does not implementSized
)unsize
: Makes the pointer fat. The data pointer is still stored therein, and pointee-specific metadata is added.
- type ascription (That is, the fact that
None as Option<u8>
compiles)ascribe
: This... isn't really a function. It's more like a special inference thing.
Also, here's some special mentions:
- char -> u8: Desugars to
char -> u32 -> u8
. That is, it truncates the character. - &mut T -> *const T. Desugars to
&mut T -> &T -> *const T
. Notably, this means that if the resulting pointer is cast back to*mut T
, it cannot be used for writes anyway.