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Jul 1, 2015
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fmt: Update docs and mention :#? pretty-printing #26678

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45 changes: 23 additions & 22 deletions src/libcollections/fmt.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -128,15 +128,15 @@
//! This allows multiple actual types to be formatted via `{:x}` (like `i8` as
//! well as `isize`). The current mapping of types to traits is:
//!
//! * *nothing* ⇒ `Display`
//! * `?` ⇒ `Debug`
//! * `o` ⇒ `Octal`
//! * `x` ⇒ `LowerHex`
//! * `X` ⇒ `UpperHex`
//! * `p` ⇒ `Pointer`
//! * `b` ⇒ `Binary`
//! * `e` ⇒ `LowerExp`
//! * `E` ⇒ `UpperExp`
//! * *nothing* ⇒ [`Display`](trait.Display.html)
//! * `?` ⇒ [`Debug`](trait.Debug.html)
//! * `o` ⇒ [`Octal`](trait.Octal.html)
//! * `x` ⇒ [`LowerHex`](trait.LowerHex.html)
//! * `X` ⇒ [`UpperHex`](trait.UpperHex.html)
//! * `p` ⇒ [`Pointer`](trait.Pointer.html)
//! * `b` ⇒ [`Binary`](trait.Binary.html)
//! * `e` ⇒ [`LowerExp`](trait.LowerExp.html)
//! * `E` ⇒ [`UpperExp`](trait.UpperExp.html)
//!
//! What this means is that any type of argument which implements the
//! `fmt::Binary` trait can then be formatted with `{:b}`. Implementations
Expand Down Expand Up @@ -367,11 +367,11 @@
//! should always be printed.
//! * '-' - Currently not used
//! * '#' - This flag is indicates that the "alternate" form of printing should
//! be used. For array slices, the alternate form omits the brackets.
//! For the integer formatting traits, the alternate forms are:
//! be used. The alternate forms are:
//! * `#?` - pretty-print the `Debug` formatting
//! * `#x` - precedes the argument with a "0x"
//! * `#X` - precedes the argument with a "0x"
//! * `#t` - precedes the argument with a "0b"
//! * `#b` - precedes the argument with a "0b"
//! * `#o` - precedes the argument with a "0o"
//! * '0' - This is used to indicate for integer formats that the padding should
//! both be done with a `0` character as well as be sign-aware. A format
Expand Down Expand Up @@ -408,19 +408,20 @@
//!
//! There are three possible ways to specify the desired `precision`:
//!
//! There are three possible ways to specify the desired `precision`:
//! 1. An integer `.N`,
//! 2. an integer followed by dollar sign `.N$`, or
//! 3. an asterisk `.*`.
//! 1. An integer `.N`:
//!
//! the integer `N` itself is the precision.
//!
//! 2. An integer followed by dollar sign `.N$`:
//!
//! The first specification, `.N`, means the integer `N` itself is the precision.
//! use format *argument* `N` (which must be a `usize`) as the precision.
//!
//! The second, `.N$`, means use format *argument* `N` (which must be a `usize`) as the precision.
//! 3. An asterisk `.*`:
//!
//! Finally, `.*` means that this `{...}` is associated with *two* format inputs rather than one:
//! the first input holds the `usize` precision, and the second holds the value to print. Note
//! that in this case, if one uses the format string `{<arg>:<spec>.*}`, then the `<arg>` part
//! refers to the *value* to print, and the `precision` must come in the input preceding `<arg>`.
//! `.*` means that this `{...}` is associated with *two* format inputs rather than one: the
//! first input holds the `usize` precision, and the second holds the value to print. Note that
//! in this case, if one uses the format string `{<arg>:<spec>.*}`, then the `<arg>` part refers
//! to the *value* to print, and the `precision` must come in the input preceding `<arg>`.
//!
//! For example, these:
//!
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5 changes: 4 additions & 1 deletion src/libcore/fmt/mod.rs
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Expand Up @@ -267,7 +267,7 @@ impl<'a> Display for Arguments<'a> {
}
}

/// Format trait for the `:?` format. Useful for debugging, all types
/// Format trait for the `?` character. Useful for debugging, all types
/// should implement this.
///
/// Generally speaking, you should just `derive` a `Debug` implementation.
Expand Down Expand Up @@ -312,6 +312,9 @@ impl<'a> Display for Arguments<'a> {
/// There are a number of `debug_*` methods on `Formatter` to help you with manual
/// implementations, such as [`debug_struct`][debug_struct].
///
/// `Debug` implementations using either `derive` or the debug builder API
/// on `Formatter` support pretty printing using the alternate flag: `{:#?}`.
///
/// [debug_struct]: ../std/fmt/struct.Formatter.html#method.debug_struct
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_on_unimplemented = "`{Self}` cannot be formatted using `:?`; if it is \
Expand Down