Implement Object#tap

mrbgems/mruby-object-ext/mrblib/object.rb

@@ -0,0 +1,19 @@
+class Object
+  ##
+  #  call-seq:
+  #     obj.tap{|x|...}    -> obj
+  #
+  #  Yields <code>x</code> to the block, and then returns <code>x</code>.
+  #  The primary purpose of this method is to "tap into" a method chain,
+  #  in order to perform operations on intermediate results within the chain.
+  #
+  #  (1..10)                .tap {|x| puts "original: #{x.inspect}"}
+  #    .to_a                .tap {|x| puts "array: #{x.inspect}"}
+  #    .select {|x| x%2==0} .tap {|x| puts "evens: #{x.inspect}"}
+  #    .map { |x| x*x }     .tap {|x| puts "squares: #{x.inspect}"}
+  #
+  def tap
+    yield self
+    self
+  end
+end

mrbgems/mruby-object-ext/test/object.rb

@@ -7,3 +7,19 @@ assert('Object#instance_exec') do
   k = KlassWithSecret.new
   assert_equal 104, k.instance_exec(5) {|x| @secret+x }
 end
+
+assert('Object#tap') do
+  ret = []
+  (1..10)                 .tap {|x| ret << "original: #{x.inspect}"}
+     .to_a                .tap {|x| ret << "array: #{x.inspect}"}
+     .select {|x| x%2==0} .tap {|x| ret << "evens: #{x.inspect}"}
+     .map { |x| x*x }     .tap {|x| ret << "squares: #{x.inspect}"}
+
+  assert_equal [
+    "original: 1..10",
+    "array: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]",
+    "evens: [2, 4, 6, 8, 10]",
+    "squares: [4, 16, 36, 64, 100]"
+  ], ret
+  assert_equal(:tap_ok, Class.new {def m; tap{return :tap_ok}; end}.new.m)
+end