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# -*- coding: utf-8; frozen_string_literal: true -*-
#
#--
# Copyright (C) 2009-2019 Thomas Leitner <t_leitner@gmx.at>
#
# This file is part of kramdown which is licensed under the MIT.
#++
#
module Kramdown
module Utils
# A simple least recently used (LRU) cache.
#
# The cache relies on the fact that Ruby's Hash class maintains insertion order. So deleting
# and re-inserting a key-value pair on access moves the key to the last position. When an
# entry is added and the cache is full, the first entry is removed.
class LRUCache
# Creates a new LRUCache that can hold +size+ entries.
def initialize(size)
@size = size
@cache = {}
end
# Returns the stored value for +key+ or +nil+ if no value was stored under the key.
def [](key)
(val = @cache.delete(key)).nil? ? nil : @cache[key] = val
end
# Stores the +value+ under the +key+.
def []=(key, value)
@cache.delete(key)
@cache[key] = value
@cache.shift if @cache.length > @size
end
end
end
end
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