1 unstable release
Uses old Rust 2015
0.0.1 | Apr 13, 2015 |
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#7 in #upcast
6KB
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This module defines a trait UpCastAs<T>
which allows one to upcast (as in only types which make sense
and can fit it another are allowed) between primitive types. These follow a simple hierarchy:
f64 > f32 > u64 > u32 > u16 > u8
f64 > f32 > i64 > i32 > i16 > i8
Signed and unsigned types don't mix well. You can see these as implication rules, as in a type
which is UpCastAs<u64>
implies it can be cast from u32
since u64 > u32
. And in this
scheme, UpCastAs<f64>
means it can be cast from a f64
, which would mean it can be up cast
from any number type.
Examples
Examples of cast
:
fn example<T: UpCastAs<u32>>() {
let _: T = cast(10u8);
let _ = cast::<u8, T>(10u8); // Alternate syntax, uglier.
let _: T = cast(10u16);
let _: T = cast(10u32);
let _: T = cast(10u64); // Error, u64 > u32
let _: T = cast(10f32); // Error, f32 > u32
let _: T = cast(10f64); // Error, f32 > u32
}
cast
is just a thin wrapper around UpCastAs::from
:
fn example<T: UpCastAs<u32>>() {
let _: T = UpCastAs::from(10u8);
let _: T = UpCastAs::from(10u16);
// ...
}
You can also call from directly from T
, but it will not follow the implication rules, it'll
only recognize casting from V
if T: UpCastAs<V>
, so this is not recommended:
fn example<T: UpCastAs<u32>>() {
let _ = T::from(10u16); // Error
let _ = T::from(10u32);
let _ = T::from(10u64); // Error.
}