diff options
| -rw-r--r-- | library/alloc/src/fmt.rs | 17 | ||||
| -rw-r--r-- | library/alloc/src/lib.rs | 1 |
2 files changed, 18 insertions, 0 deletions
diff --git a/library/alloc/src/fmt.rs b/library/alloc/src/fmt.rs index 50e789d76b7..b4d16d74db4 100644 --- a/library/alloc/src/fmt.rs +++ b/library/alloc/src/fmt.rs @@ -17,6 +17,8 @@ //! format!("The number is {}", 1); // => "The number is 1" //! format!("{:?}", (3, 4)); // => "(3, 4)" //! format!("{value}", value=4); // => "4" +//! let people = "Rustaceans"; +//! format!("Hello {people}!"); // => "Hello Rustaceans!" //! format!("{} {}", 1, 2); // => "1 2" //! format!("{:04}", 42); // => "0042" with leading zeros //! format!("{:#?}", (100, 200)); // => "( @@ -80,6 +82,19 @@ //! format!("{a} {c} {b}", a="a", b='b', c=3); // => "a 3 b" //! ``` //! +//! If a named parameter does not appear in the argument list, `format!` will +//! reference a variable with that name in the current scope. +//! +//! ``` +//! let argument = 2 + 2; +//! format!("{argument}"); // => "4" +//! +//! fn make_string(a: u32, b: &str) -> String { +//! format!("{b} {a}") +//! } +//! make_string(927, "label"); // => "label 927" +//! ``` +//! //! It is not valid to put positional parameters (those without names) after //! arguments that have names. Like with positional parameters, it is not //! valid to provide named parameters that are unused by the format string. @@ -98,6 +113,8 @@ //! println!("Hello {:1$}!", "x", 5); //! println!("Hello {1:0$}!", 5, "x"); //! println!("Hello {:width$}!", "x", width = 5); +//! let width = 5; +//! println!("Hello {:width$}!", "x"); //! ``` //! //! This is a parameter for the "minimum width" that the format should take up. diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs index 1bb257acff7..746dd50ad22 100644 --- a/library/alloc/src/lib.rs +++ b/library/alloc/src/lib.rs @@ -105,6 +105,7 @@ #![feature(fmt_internals)] #![feature(fn_traits)] #![feature(inherent_ascii_escape)] +#![feature(format_args_capture)] #![feature(inplace_iteration)] #![feature(iter_advance_by)] #![feature(iter_zip)] |