From 94d5416db6415b06706204fb4a4df0100bcab7be Mon Sep 17 00:00:00 2001 From: Yorick Peterse <yorickpeterse@gmail.com> Date: Thu, 26 May 2016 13:13:57 +0200 Subject: [PATCH] Added Gitlab::Lazy This class can be used to lazy-evaluate blocks of code the first time they're called. This can be useful when a method performs a certain heavy operation (e.g. a SQL query) that you only want to perform whenever the result is used for the first time. --- lib/gitlab/lazy.rb | 34 +++++++++++++++++++++++++++++++++ spec/lib/gitlab/lazy_spec.rb | 37 ++++++++++++++++++++++++++++++++++++ 2 files changed, 71 insertions(+) create mode 100644 lib/gitlab/lazy.rb create mode 100644 spec/lib/gitlab/lazy_spec.rb diff --git a/lib/gitlab/lazy.rb b/lib/gitlab/lazy.rb new file mode 100644 index 00000000000..2a659ae4c74 --- /dev/null +++ b/lib/gitlab/lazy.rb @@ -0,0 +1,34 @@ +module Gitlab + # A class that can be wrapped around an expensive method call so it's only + # executed when actually needed. + # + # Usage: + # + # object = Gitlab::Lazy.new { some_expensive_work_here } + # + # object['foo'] + # object.bar + class Lazy < BasicObject + def initialize(&block) + @block = block + end + + def method_missing(name, *args, &block) + __evaluate__ + + @result.__send__(name, *args, &block) + end + + def respond_to_missing?(name, include_private = false) + __evaluate__ + + @result.respond_to?(name, include_private) || super + end + + private + + def __evaluate__ + @result = @block.call unless defined?(@result) + end + end +end diff --git a/spec/lib/gitlab/lazy_spec.rb b/spec/lib/gitlab/lazy_spec.rb new file mode 100644 index 00000000000..b5ca89dd242 --- /dev/null +++ b/spec/lib/gitlab/lazy_spec.rb @@ -0,0 +1,37 @@ +require 'spec_helper' + +describe Gitlab::Lazy, lib: true do + let(:dummy) { double(:dummy) } + + context 'when not calling any methods' do + it 'does not call the supplied block' do + expect(dummy).not_to receive(:foo) + + described_class.new { dummy.foo } + end + end + + context 'when calling a method on the object' do + it 'lazy loads the value returned by the block' do + expect(dummy).to receive(:foo).and_return('foo') + + lazy = described_class.new { dummy.foo } + + expect(lazy.to_s).to eq('foo') + end + end + + describe '#respond_to?' do + it 'returns true for a method defined on the wrapped object' do + lazy = described_class.new { 'foo' } + + expect(lazy).to respond_to(:downcase) + end + + it 'returns false for a method not defined on the wrapped object' do + lazy = described_class.new { 'foo' } + + expect(lazy).not_to respond_to(:quack) + end + end +end -- 2.30.9