Macro rumtk_cache_fetch 

macro_rules! rumtk_cache_fetch {
    ( $cache:expr, $key:expr, $func:expr ) => { ... };
}

Searches for item in global cache. If global cache lacks item, create item using factory function passed to this macro.

use crate::rumtk_core::rumtk_cache_fetch;
use crate::rumtk_core::cache::{new_cache, LazyRUMCache};
use std::sync::Arc;

type StringCache = LazyRUMCache<String, String>;

fn init_cache(k: &String) -> String {
   String::from(k)
}

let mut cache: StringCache = new_cache();

let test_key: String = String::from("Hello World");
let v = rumtk_cache_fetch!(
    &mut cache,
    &test_key,
    init_cache
);

assert_eq!(test_key.as_str(), v.as_str(), "The inserted key is not the same to what was passed as input!");