class Cache::LRU {
    use Hash::Ordered;
    
    has $cache    :handles(get)  :builder;
    has $max_size :new(optional) :reader :isa(PositiveInt) = 20;
    has $created  :reader = time;

    method _build_cache () { Hash::Ordered->new }

    method set ( $key, $value ) {
        if ( $cache->exists($key) ) {
            $cache->delete($key);
        } 
        elsif ( $cache->keys > $max_size ) {
            $cache->shift;
        }
        $cache->set( $key, $value );  # new values in front
    }
}