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.

1 files changed, 34 insertions, 0 deletions

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