Add LazyObject class.

Library/Homebrew/lazy_object.rb

@@ -0,0 +1,14 @@
+class LazyObject < Delegator
+  def initialize(&callable)
+    super(callable)
+  end
+
+  def __getobj__
+    return @__delegate__ if defined?(@__delegate__)
+    @__delegate__ = @__callable__.call
+  end
+
+  def __setobj__(callable)
+    @__callable__ = callable
+  end
+end

Library/Homebrew/test/lazy_object_spec.rb

@@ -0,0 +1,35 @@
+require "lazy_object"
+
+describe LazyObject do
+  describe "#initialize" do
+    it "does not evaluate the block" do
+      expect { |block|
+        described_class.new(&block)
+      }.not_to yield_control
+    end
+  end
+
+  describe "when receiving a message" do
+    it "evaluates the block" do
+      expect(described_class.new { 42 }.to_s).to eq "42"
+    end
+  end
+
+  describe "#!" do
+    it "delegates to the underlying object" do
+      expect(!(described_class.new { false })).to be true
+    end
+  end
+
+  describe "#!=" do
+    it "delegates to the underlying object" do
+      expect(described_class.new { 42 }).not_to eq 13
+    end
+  end
+
+  describe "#==" do
+    it "delegates to the underlying object" do
+      expect(described_class.new { 42 }).to eq 42
+    end
+  end
+end