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Interior mutability, write-once and borrowable as plain `&T`
------------------------------------------------------------
This library provides interior mutability that can be borrowed
as plain immutable references `&T` in exchange for the write-once,
read-many restriction.
Unlike `std::cell::Cell` or `std::cell::RefCell`, a plain immutable
reference `&T` can be taken from `MutOnce<T>`. Once an immutable
reference is taken, the value can never be mutated (even after all
references are dropped).
The use cases include caching getter and delayed evaluation.
Usage
-----
Run "cargo doc" in the source directory to generate the API reference.
It is also available online at <https://docs.rs/mutate_once>.
An example follows:
struct Container {
expensive: MutOnce<String>,
}
impl Container {
fn expensive(&self) -> &str {
if !self.expensive.is_fixed() {
let mut ref_mut = self.expensive.get_mut();
*ref_mut += "expensive";
// Drop `ref_mut` before calling `get_ref`.
}
// A plain reference can be returned to the caller
// unlike `Cell` or `RefCell`.
self.expensive.get_ref()
}
}
let container = Container { expensive: MutOnce::new(String::new()) };
assert_eq!(container.expensive(), "expensive");
|
