pub trait PrimitiveFrom<T>: 'static + Copy
where
T: 'static + Copy,
{
fn from(_:T) -> Self;
}
macro_rules! impl_primitive_from {
($U: ty => $( $T: ty ),* ) => {
$(
impl PrimitiveFrom<$U> for $T {
#[inline] fn from(a:$U) -> $T { a as $T }
}
)*
};
}
impl_primitive_from!(u8 => char, u8, i8, u16, i16, u32, i32, u64, isize, usize, i64, f32, f64);
impl_primitive_from!(i8 => u8, i8, u16, i16, u32, i32, u64, isize, usize, i64, f32, f64);
impl_primitive_from!(u16 => u8, i8, u16, i16, u32, i32, u64, isize, usize, i64, f32, f64);
impl_primitive_from!(i16 => u8, i8, u16, i16, u32, i32, u64, isize, usize, i64, f32, f64);
impl_primitive_from!(u32 => u8, i8, u16, i16, u32, i32, u64, isize, usize, i64, f32, f64);
impl_primitive_from!(i32 => u8, i8, u16, i16, u32, i32, u64, isize, usize, i64, f32, f64);
impl_primitive_from!(u64 => u8, i8, u16, i16, u32, i32, u64, isize, usize, i64, f32, f64);
impl_primitive_from!(i64 => u8, i8, u16, i16, u32, i32, u64, isize, usize, i64, f32, f64);
impl_primitive_from!(usize => u8, i8, u16, i16, u32, i32, u64, isize, usize, i64, f32, f64);
impl_primitive_from!(isize => u8, i8, u16, i16, u32, i32, u64, isize, usize, i64, f32, f64);
impl_primitive_from!(f32 => u8, i8, u16, i16, u32, i32, u64, isize, usize, i64, f32, f64);
impl_primitive_from!(f64 => u8, i8, u16, i16, u32, i32, u64, isize, usize, i64, f32, f64);
impl_primitive_from!(char => char, u8, i8, u16, i16, u32, i32, u64, isize, usize, i64);
impl_primitive_from!(bool => u8, i8, u16, i16, u32, i32, u64, isize, usize, i64);
#[test]
fn as_primitive() {
let x: f32 = PrimitiveFrom::from(1.625f64);
assert_eq!(x, 1.625f32);
let x: f32 = PrimitiveFrom::from(3.14159265358979323846f64);
assert_eq!(x, 3.1415927f32);
let x: u8 = PrimitiveFrom::from(768i16);
assert_eq!(x, 0);
}