Cache::LRU

LRU.pm6

use v6;
class Cache::LRU {
  has Hash[Node] %.entries;
  has Node $.lru;
  
  class Node {
    has $value is required;
    has $prev is rw;
    has $next is rw;
    method splice() {
      return unless defined $next;
      $next.prev = $prev;
      $prev.next = $next;
      $prev = $next = Nil;
    }
    method put-before-me(Node $newest) {
      die if defined $newest.prev or defined $newest.next;
      $newest.next = self;
      $newest.prev = $.prev;
      $.prev.next = $newest;
      $.prev = $newest;
    }
  }
  
  method _delete( $key ) {
    my $node = %.entries{$key} :delete or return;
    if $node === $lru {
      if $node.next === $node {
        $lru = Nil;
      } else {
        $lru = $lru.next;
      }
    }
    return $node.splice;
  }
  
  method delete( $key ) {
    my $node = _delete( $key );
    return $node ? $node.value : Nil;
  }
  
  method set( $key, $value ) {
    my $node = _delete( $key );
    if $node {
      $node.value = $value
    } else {
      $node = Node.new($:value)
    }
    if $lru {
      $lru.put-before-me( $node );
    } else {
      $lru = $node;
    }
    $value;
  }
  
  method delete-lru() {
    self._delete( $lru ) if defined $lru;
  }
};