Struct frame_support::dispatch::fmt::Arguments

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

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 the write() and format() functions can be safely performed.

You can use the Arguments<'a> that format_args! returns in Debug and Display contexts as seen below. The example also shows that Debug and 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);

Implementations

impl<'a> Arguments<'a>

pub fn as_str(&self) -> Option<&'static str>

🔬 This is a nightly-only experimental API. (fmt_as_str)

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

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

Examples

#![feature(fmt_as_str)]

use core::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());
    }
}

#![feature(fmt_as_str)]

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

Trait Implementations

impl<'a> Clone for Arguments<'a>

fn clone(&self) -> Arguments<'a>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<'a> Copy for Arguments<'a>

impl<'_> Debug for Arguments<'_>

fn fmt(&self, fmt: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<'_> Display for Arguments<'_>

fn fmt(&self, fmt: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<'a> Serialize for Arguments<'a>

fn serialize<S>(
    &self,
    serializer: S
) -> Result<<S as Serializer>::Ok, <S as Serializer>::Error> where
    S: Serializer, 

Serialize this value into the given Serde serializer.

impl<'a> Value for Arguments<'a>

fn record(&self, key: &Field, visitor: &mut dyn Visit)

Visits this value with the given Visitor.