Trait DefaultMap

pub trait DefaultMap: Map<V: Default + Eq> {
    // Provided method
    fn entry_or_default(
        &mut self,
        k: Self::K,
    ) -> DefaultEntry<'_, Self::VacantEntry<'_>, Self::OccupiedEntry<'_>> { ... }
}

A mapping where non-existing keys considered to have Default values

Provided Methods

fn entry_or_default( &mut self, k: Self::K, ) -> DefaultEntry<'_, Self::VacantEntry<'_>, Self::OccupiedEntry<'_>>

Get an entry at given key or Default value if the key doesn’t exist.

The returned entry will automatically be removed from the map if it becomes equal to Default after modifications.

Example

let mut m = HashMap::new();
*m.entry_or_default("a") += 1;
assert_eq!(m.get("a"), Some(&1));
*m.entry_or_default("a") -= 1;
assert_eq!(m.get("a"), None);

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> DefaultMap for T

where T: Map<V: Default + Eq>,