Arguments in alloc::fmt - Rust
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.
Keywords: rust, rustlang, rust-lang, Arguments

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

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

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);

Run

## Implementations

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### impl<'a> Arguments<'a>

1.52.0 (const: unstable)[src]

#### 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());
        }
    }

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

## Trait Implementations

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

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

Returns a copy of the value. Read more

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

Performs copy-assignment from `source`. Read more

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

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

Formats the value using the given formatter. Read more

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

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

Formats the value using the given formatter. Read more

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### 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

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### impl<T> Any for T where
T: 'static + ?Sized,

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#### pub fn type_id(&self) -> TypeId

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

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### impl<T> Borrow<T> for T where
T: ?Sized,

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#### pub fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more

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### impl<T> BorrowMut<T> for T where
T: ?Sized,

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#### pub fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more

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### impl<T> From<T> for T

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#### pub fn from(t: T) -> T

Performs the conversion.

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### impl<T, U> Into<U> for T where
U: From<T>,

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#### pub fn into(self) -> U

Performs the conversion.

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### impl<T> ToOwned for T where
T: Clone,

#### type Owned = T

The resulting type after obtaining ownership.

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#### pub fn to_owned(&Self) -> T

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

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#### pub fn clone_into(&Self, &mut T)

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

recently added

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

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### impl<T> ToString for T where
T: Display + ?Sized,

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#### pub default fn to_string(&Self) -> String

Converts the given value to a `String`. Read more

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### impl<T, U> TryFrom<U> for T where
U: Into<T>,

#### type Error = Infallible

The type returned in the event of a conversion error.

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#### pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.

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### impl<T, U> TryInto<U> for T where
U: TryFrom<T>,

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

The type returned in the event of a conversion error.

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#### pub fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.