# Struct core::fmt::Arguments 1.0.0[−][src]

    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);

Run

## Implementations

### `impl<'a> Arguments<'a>`[src]

#### `pub fn as_str(&self) -> Option<&'static str>`[src]

🔬 This is a nightly-only experimental API. (`fmt_as_str` #74442)

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 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

    #![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);

Run

## Trait Implementations

### `impl<'a> Clone for Arguments<'a>`[src]

#### `fn clone(&self) -> Arguments<'a>`[src]

Returns a copy of the value. Read more

#### `fn clone_from(&mut self, source: &Self)`[src]

Performs copy-assignment from `source`. Read more

### `impl<'a> Copy for Arguments<'a>`[src]

### `impl Debug for Arguments<'_>`[src]

#### `fn fmt(&self, fmt: &mut Formatter<'_>) -> Result`[src]

Formats the value using the given formatter. Read more

### `impl Display for Arguments<'_>`[src]

#### `fn fmt(&self, fmt: &mut Formatter<'_>) -> Result`[src]

Formats the value using the given formatter. Read more

## Auto Trait Implementations

### `impl<'a> !Send for Arguments<'a>`[src]

### `impl<'a> !Sync for Arguments<'a>`[src]

### `impl<'a> Unpin for Arguments<'a>`[src]

## Blanket Implementations

### `impl<T> Any for T where
T: 'static + ?Sized,` [src]

#### `pub fn type_id(&Self) -> TypeId`[src]

Gets the `TypeId` of `self`. Read more

### `impl<T> Borrow<T> for T where
T: ?Sized,` [src]

#### `pub fn borrow(&Self) -> &T`[src]

Immutably borrows from an owned value. Read more

### `impl<T> BorrowMut<T> for T where
T: ?Sized,` [src]

#### `pub fn borrow_mut(&mut Self) -> &mut T`[src]

Mutably borrows from an owned value. Read more

### `impl<T> From<T> for T`[src]

#### `pub fn from(T) -> T`[src]

Performs the conversion.

### `impl<T, U> Into<U> for T where
U: From<T>,` [src]

#### `pub fn into(Self) -> U`[src]

Performs the conversion.

### `impl<T, U> TryFrom<U> for T where
U: Into<T>,` [src]

#### `type Error = Infallible`

The type returned in the event of a conversion error.

#### `pub fn try_from(U) -> Result<T, <T as TryFrom<U>>::Error>`[src]

Performs the conversion.

### `impl<T, U> TryInto<U> for T where
U: TryFrom<T>,` [src]

#### `type Error = <U as TryFrom<T>>::Error`

The type returned in the event of a conversion error.

#### `pub fn try_into(Self) -> Result<U, <U as TryFrom<T>>::Error>`[src]

Performs the conversion.