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 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);
RunImplementations
sourceimpl<'a> Arguments<'a>
impl<'a> Arguments<'a>
1.52.0 (const: unstable) · sourcepub fn as_str(&self) -> Option<&'static str>
pub fn as_str(&self) -> Option<&'static 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
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());
}
}
Runassert_eq!(format_args!("hello").as_str(), Some("hello"));
assert_eq!(format_args!("").as_str(), Some(""));
assert_eq!(format_args!("{}", 1).as_str(), None);
RunTrait Implementations
impl<'a> Copy for Arguments<'a>
Auto Trait Implementations
impl<'a> !RefUnwindSafe for Arguments<'a>
impl<'a> !Send for Arguments<'a>
impl<'a> !Sync for Arguments<'a>
impl<'a> Unpin for Arguments<'a>
impl<'a> !UnwindSafe for Arguments<'a>
Blanket Implementations
sourceimpl<T> BorrowMut<T> for T where
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more
sourceimpl<T> ToOwned for T where
T: Clone,
impl<T> ToOwned for T where
T: Clone,
type Owned = T
type Owned = T
The resulting type after obtaining ownership.
sourcefn clone_into(&self, target: &mut T)
fn clone_into(&self, target: &mut T)
Uses borrowed data to replace owned data, usually by cloning. Read more