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Document non-obvious behavior of fmt::UpperHex & co for negative integers #46285

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Nov 28, 2017
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Document non-obvious behavior of fmt::UpperHex & co for negative integers #46285

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20 changes: 20 additions & 0 deletions src/libcore/fmt/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -624,6 +624,9 @@ pub trait Display {
///
/// The `Octal` trait should format its output as a number in base-8.
///
/// For primitive signed integers (`i8` to `i128`, and `isize`),
/// negative values are formatted as the two’s complement representation.
///
/// The alternate flag, `#`, adds a `0o` in front of the output.
///
/// For more information on formatters, see [the module-level documentation][module].
Expand All @@ -639,6 +642,8 @@ pub trait Display {
///
/// assert_eq!(format!("{:o}", x), "52");
/// assert_eq!(format!("{:#o}", x), "0o52");
///
/// assert_eq!(format!("{:o}", -16), "37777777760");
/// ```
///
/// Implementing `Octal` on a type:
Expand Down Expand Up @@ -671,6 +676,9 @@ pub trait Octal {
///
/// The `Binary` trait should format its output as a number in binary.
///
/// For primitive signed integers (`i8` to `i128`, and `isize`),
/// negative values are formatted as the two’s complement representation.
///
/// The alternate flag, `#`, adds a `0b` in front of the output.
///
/// For more information on formatters, see [the module-level documentation][module].
Expand All @@ -686,6 +694,8 @@ pub trait Octal {
///
/// assert_eq!(format!("{:b}", x), "101010");
/// assert_eq!(format!("{:#b}", x), "0b101010");
///
/// assert_eq!(format!("{:b}", -16), "11111111111111111111111111110000");
/// ```
///
/// Implementing `Binary` on a type:
Expand Down Expand Up @@ -719,6 +729,9 @@ pub trait Binary {
/// The `LowerHex` trait should format its output as a number in hexadecimal, with `a` through `f`
/// in lower case.
///
/// For primitive signed integers (`i8` to `i128`, and `isize`),
/// negative values are formatted as the two’s complement representation.
///
/// The alternate flag, `#`, adds a `0x` in front of the output.
///
/// For more information on formatters, see [the module-level documentation][module].
Expand All @@ -734,6 +747,8 @@ pub trait Binary {
///
/// assert_eq!(format!("{:x}", x), "2a");
/// assert_eq!(format!("{:#x}", x), "0x2a");
///
/// assert_eq!(format!("{:x}", -16), "fffffff0");
/// ```
///
/// Implementing `LowerHex` on a type:
Expand Down Expand Up @@ -767,6 +782,9 @@ pub trait LowerHex {
/// The `UpperHex` trait should format its output as a number in hexadecimal, with `A` through `F`
/// in upper case.
///
/// For primitive signed integers (`i8` to `i128`, and `isize`),
/// negative values are formatted as the two’s complement representation.
///
/// The alternate flag, `#`, adds a `0x` in front of the output.
///
/// For more information on formatters, see [the module-level documentation][module].
Expand All @@ -782,6 +800,8 @@ pub trait LowerHex {
///
/// assert_eq!(format!("{:X}", x), "2A");
/// assert_eq!(format!("{:#X}", x), "0x2A");
///
/// assert_eq!(format!("{:X}", -16), "FFFFFFF0");
/// ```
///
/// Implementing `UpperHex` on a type:
Expand Down