Trait EntryInsertExt

pub trait EntryInsertExt<'a, K, V> {
    // Required methods
    fn or_try_insert_with<F: FnOnce() -> Result<V, E>, E>(
        self,
        default: F,
    ) -> Result<&'a mut V, E>;
    fn or_try_insert_with_key<F: FnOnce(&K) -> Result<V, E>, E>(
        self,
        default: F,
    ) -> Result<&'a mut V, E>;
}

Extends map entries with or_try_insert_with and or_try_insert_with_key.

Required Methods

fn or_try_insert_with<F: FnOnce() -> Result<V, E>, E>( self, default: F, ) -> Result<&'a mut V, E>

If empty, computes the value from the default function. If the function returns Ok, inserts the value. If f returns Err, returns the error. If there is no error, returns a mutable reference to the value in the entry.

Examples

use std::collections::HashMap;

use try_insert_ext::EntryInsertExt;

let mut map: HashMap<&str, String> = HashMap::new();
let s = "hoho".to_string();

let e: Result<&mut String, ()> = map
    .entry("poneyland")
    .or_try_insert_with(|| Err(()));
assert!(e.is_err());
map.entry("poneyland").or_try_insert_with::<_, ()>(|| Ok(s));

assert_eq!(map["poneyland"], "hoho".to_string());

fn or_try_insert_with_key<F: FnOnce(&K) -> Result<V, E>, E>( self, default: F, ) -> Result<&'a mut V, E>

If empty, computes the value from the default function. If the function returns Ok, inserts the value. If f returns Err, returns the error. If there is no error, returns a mutable reference to the value in the entry. This method allows for generating key-derived values for insertion by providing the default function a reference to the key that was moved during the .entry(key) method call.

Examples

use std::collections::HashMap;

use try_insert_ext::EntryInsertExt;

let mut map: HashMap<&str, usize> = HashMap::new();

let e: Result<&mut usize, ()> = map
    .entry("poneyland")
    .or_try_insert_with_key(|_| Err(()));
assert!(e.is_err());
map
    .entry("poneyland")
    .or_try_insert_with_key::<_, ()>(|key| Ok(key.chars().count()));

assert_eq!(map["poneyland"], 9);

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.

Implementations on Foreign Types

impl<'a, K, V> EntryInsertExt<'a, K, V> for Entry<'a, K, V>

where K: Ord,

fn or_try_insert_with<F: FnOnce() -> Result<V, E>, E>( self, default: F, ) -> Result<&'a mut V, E>

fn or_try_insert_with_key<F: FnOnce(&K) -> Result<V, E>, E>( self, default: F, ) -> Result<&'a mut V, E>

impl<'a, K, V> EntryInsertExt<'a, K, V> for Entry<'a, K, V>

fn or_try_insert_with<F: FnOnce() -> Result<V, E>, E>( self, default: F, ) -> Result<&'a mut V, E>

fn or_try_insert_with_key<F: FnOnce(&K) -> Result<V, E>, E>( self, default: F, ) -> Result<&'a mut V, E>

Implementors