pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V {
        match self {
            Occupied(entry) => entry.into_mut(),
            Vacant(entry) => entry.insert(default()),
        }
    }
/// Ensures a value is in the entry by inserting the result of the default function if empty,
/// and returns a mutable reference to the value in the entry.
///
/// # Examples
///
/// ```
/// use std::collections::HashMap;
///
/// let mut map: HashMap<&str, String> = HashMap::new();
/// let s = "hoho".to_string();
///
/// map.entry("poneyland").or_insert_with(|| s);
///
/// assert_eq!(map["poneyland"], "hoho".to_string());
/// ```
Ensures a value is in the entry by inserting the result of the default function if empty,
and returns a mutable reference to the value in the entry.
Ensures a value is in the entry by inserting the result of the default function if empty and returns a mutable reference to the value in the entry .
pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V {
        match self {
            Occupied(entry) => entry.into_mut(),
            Vacant(entry) => entry.insert(default()),
        }
    }
pub fn or_insert_with < F : FnOnce ( ) -> V > ( self , default : F ) -> & ' a mut V { match self { Occupied ( entry ) => entry . into_mut ( ) , Vacant ( entry ) => entry . insert ( default ( ) ) , } }
Ensures a value is in the entry by inserting the result of the default function if empty,
and returns a mutable reference to the value in the entry.
Ensures a value is in the entry by inserting the result of the default function if empty and returns a mutable reference to the value in the entry .
self
default
F
examples
```
use std::collections::HashMap.

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

map.entry("poneyland").or_insert_with(|| s).


` ` ` use std :: collections :: HashMap . let mut map : HashMap<&str String > = HashMap :: new () ; let s = " hoho " . to_string () . map . entry ( " poneyland " ) . or_insert_with ( || s ) .