Arguments in std::fmt - Rust (original) (raw)

pub struct Arguments<'a> { /* private fields */ }

Expand description

This structure represents a safely precompiled version of a format string and its arguments. This cannot be generated at runtime because it cannot safely be done, so no constructors are given and the fields are private to prevent modification.

The format_args! macro will safely create an instance of this structure. The macro validates the format string at compile-time so usage of thewrite() and format() functions can be safely performed.

You can use the Arguments<'a> that format_args! returns in Debugand Display contexts as seen below. The example also shows that Debugand Display format to the same thing: the interpolated format string in format_args!.

let debug = format!("{:?}", format_args!("{} foo {:?}", 1, 2));
let display = format!("{}", format_args!("{} foo {:?}", 1, 2));
assert_eq!("1 foo 2", display);
assert_eq!(display, debug);

Run

1.52.0 (const: unstable) · source

Get the formatted string, if it has no arguments to be formatted.

This can be used to avoid allocations in the most trivial case.

use std::fmt::Arguments;

fn write_str(_: &str) { /* ... */ }

fn write_fmt(args: &Arguments) {
    if let Some(s) = args.as_str() {
        write_str(s)
    } else {
        write_str(&args.to_string());
    }
}

Run

assert_eq!(format_args!("hello").as_str(), Some("hello"));
assert_eq!(format_args!("").as_str(), Some(""));
assert_eq!(format_args!("{}", 1).as_str(), None);

Run

Formats the value using the given formatter. Read more

Formats the value using the given formatter. Read more

impl Any for T where

T: 'static + ?Sized,

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

impl From for T

impl<T, U> Into for T where

U: From,

The resulting type after obtaining ownership.

Creates owned data from borrowed data, usually by cloning. Read more

🔬 This is a nightly-only experimental API. (toowned_clone_into #41263)

Uses borrowed data to replace owned data, usually by cloning. Read more

Converts the given value to a String. Read more

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.