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Auto merge of #51474 - llogiq:from-docs, r=TimNN

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add some docs to `From` conversions

This adds a helpful document to the bool → int* conversions as well as to the lossless integer conversions.

One of #51430 down, some more to go.
This commit is contained in:
bors 2018-06-10 18:00:12 +00:00
commit cabb679bf1
1 changed files with 39 additions and 13 deletions
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52
src/libcore/num/mod.rs
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@ -4709,30 +4709,56 @@ pub use num::dec2flt::ParseFloatError;
// Conversions T -> T are covered by a blanket impl and therefore excluded
// Some conversions from and to usize/isize are not implemented due to portability concerns
macro_rules! impl_from {
($Small: ty, $Large: ty, #[$attr:meta]) => {
($Small: ty, $Large: ty, #[$attr:meta], $doc: expr) => {
#[$attr]
#[doc = $doc]
impl From<$Small> for $Large {
#[inline]
fn from(small: $Small) -> $Large {
small as $Large
}
}
};
($Small: ty, $Large: ty, #[$attr:meta]) => {
impl_from!($Small,
$Large,
#[$attr],
concat!("Converts `",
stringify!($Small),
"` to `",
stringify!($Large),
"` losslessly."));
}
}
macro_rules! impl_from_bool {
($target: ty, #[$attr:meta]) => {
impl_from!(bool, $target, #[$attr], concat!("Converts a `bool` to a `",
stringify!($target), "`. The resulting value is `0` for `false` and `1` for `true`
values.
# Examples
```
assert_eq!(", stringify!($target), "::from(true), 1);
assert_eq!(", stringify!($target), "::from(false), 0);
```"));
};
}
// Bool -> Any
impl_from! { bool, u8, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from! { bool, u16, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from! { bool, u32, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from! { bool, u64, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from! { bool, u128, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from! { bool, usize, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from! { bool, i8, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from! { bool, i16, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from! { bool, i32, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from! { bool, i64, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from! { bool, i128, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from! { bool, isize, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from_bool! { u8, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from_bool! { u16, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from_bool! { u32, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from_bool! { u64, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from_bool! { u128, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from_bool! { usize, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from_bool! { i8, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from_bool! { i16, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from_bool! { i32, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from_bool! { i64, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from_bool! { i128, #[stable(feature = "from_bool", since = "1.28.0")] }
impl_from_bool! { isize, #[stable(feature = "from_bool", since = "1.28.0")] }
// Unsigned -> Unsigned
impl_from! { u8, u16, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }