Trait ExtOption

pub trait ExtOption<T>: Sealed {
    // Required methods
    fn contains<U: PartialEq<T>>(&self, x: &U) -> bool;
    fn reduce<F: FnOnce(T, T) -> T>(self, other: Option<T>, f: F) -> Option<T> ;
    fn fmt_or_empty(&self) -> OptionFmt<'_, T>;
    fn fmt_or<U: Display>(&self, u: U) -> OptionFmtOr<'_, T, U>;
    fn fmt_or_else<U: Display, F: Fn() -> U>(
        &self,
        f: F,
    ) -> OptionFmtOrElse<'_, T, F>;
}

Extension trait providing additional methods for Option.

This trait is sealed and cannot be implemented for any other type.

See also ExtResult, ExtOptRes.

Based on work from:

• https://github.com/rust-lang/rust/issues/62358 (contains).
• https://github.com/rust-lang/rust/pull/87036 (reduce).

Required Methods

fn contains<U: PartialEq<T>>(&self, x: &U) -> bool

Returns true if the option is a Some value containing the given value.

Examples

assert_eq!(Some(1).contains(&1), true);
assert_eq!(Some(1).contains(&2), false);
assert_eq!(None::<u8>.contains(&1), false);

fn reduce<F: FnOnce(T, T) -> T>(self, other: Option<T>, f: F) -> Option<T>

Merges self with another Option.

Returns

• Some(f(l, r)) if both options are Some(_).
• Some(x) if either of the options is Some(x) and the other is None.
• None if both options are None.

Examples

let (x, y) = (Some(2), Some(4));

assert_eq!(x.reduce(y, Add::add), Some(6));
assert_eq!(x.reduce(y, min), Some(2));

assert_eq!(x.reduce(None, Add::add), x);
assert_eq!(None.reduce(y, min), y);

assert_eq!(None.reduce(None, i32::add), None);

fn fmt_or_empty(&self) -> OptionFmt<'_, T>

Format some value, or display an empty string if it’s None.

Examples

assert_eq!("0x42", format!("{:#x}", Some(0x42).fmt_or_empty()));
assert_eq!("", format!("{:#x}", None::<u8>.fmt_or_empty()));

fn fmt_or<U: Display>(&self, u: U) -> OptionFmtOr<'_, T, U>

Format some value, or an alternative if it’s None.

The alternative value must implement Display regardless of which formatting is used originally.

Examples

assert_eq!("42", format!("{}", Some(Box::new(42)).fmt_or("Nothing")));
assert_eq!("Nothing", format!("{}", None::<u8>.fmt_or("Nothing")));

fn fmt_or_else<U: Display, F: Fn() -> U>( &self, f: F, ) -> OptionFmtOrElse<'_, T, F>

Format some value, or run an alternative closure if it’s None.

The value returned from the closure must implement Display regardless of which formatting is used originally.

The value returned from the closure is not stored after use. Therefore, using a single OptionFmtOrElse object for multiple formatting operations will run the closure multiple times.

Examples

assert_eq!("42", format!("{}", Some(42).fmt_or_else(|| "Nothing")));
assert_eq!("Nothing", format!("{}", None::<u8>.fmt_or_else(|| "Nothing")));

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementors

impl<T> ExtOption<T> for Option<T>