Function extern_spec_T_Option_T_get_or_insert_with 

pub fn extern_spec_T_Option_T_get_or_insert_with<T, F: FnOnce() -> T>(
    self_: &mut Option<T>,
    f: F,
) -> &mut T

extern spec for Option<T>::get_or_insert_with

This is not a real function: its only use is for documentation.

requires

self

ensures

self