From cd7ebbe54f16999b74c2c32a64336bad131ec5f3 Mon Sep 17 00:00:00 2001
From: Adam Greene <adam.greene@gmail.com>
Date: Sun, 3 May 2015 20:42:11 -0700
Subject: make repeated_field quack like an array

---
 ruby/lib/google/protobuf/repeated_field.rb | 152 ++++++++++++++++++++++++++++-
 1 file changed, 150 insertions(+), 2 deletions(-)

(limited to 'ruby/lib')

diff --git a/ruby/lib/google/protobuf/repeated_field.rb b/ruby/lib/google/protobuf/repeated_field.rb
index 5b934e56..16c843c0 100644
--- a/ruby/lib/google/protobuf/repeated_field.rb
+++ b/ruby/lib/google/protobuf/repeated_field.rb
@@ -28,12 +28,160 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-# add syntatic sugar on top of the core library
+require 'forwardable'
+
+#
+# This class makes RepeatedField act (almost-) like a Ruby Array.
+# It has convenience methods that extend the core C or Java based
+# methods.
+#
+# This is a best-effort to mirror Array behavior.  Two comments:
+#  1) patches always welcome :)
+#  2) if performance is an issue, feel free to rewrite the method
+#     in jruby and C.  The source code has plenty of examples
+#
+# KNOWN ISSUES
+#   - #[]= doesn't allow less used approaches such as `arr[1, 2] = 'fizz'`
+#   - #concat should return the orig array
+#   - #push should accept multiple arguments and push them all at the same time
+#
 module Google
   module Protobuf
     class RepeatedField
+      extend Forwardable
+
+      # methods defined in C or Java:
+      #   +
+      #   [], at
+      #   []=
+      #   concat
+      #   clear
+      #   dup, clone
+      #   each
+      #   push, <<
+      #   replace
+      #   length, size
+      #   ==
+      #   to_ary, to_a
+      #   also all enumerable
+      #
+      # NOTE:  using delegators rather than method_missing to make the
+      #        relationship explicit instead of implicit
+      def_delegators :to_ary,
+        :&, :*, :-, :'<=>',
+        :assoc, :bsearch, :combination, :compact, :count, :cycle,
+        :drop, :drop_while, :eql?, :fetch, :find_index, :flatten,
+        :include?, :index, :inspect, :join,
+        :pack, :permutation, :product, :pretty_print, :pretty_print_cycle,
+        :rassoc, :repeated_combination, :repeated_permutation, :reverse,
+        :rindex, :rotate, :sample, :shuffle, :shelljoin, :slice,
+        :to_s, :transpose, :uniq, :|
+
+
+      def first(n=nil)
+        n ? self[0..n] : self[0]
+      end
+
+
+      def last(n=nil)
+        n ? self[(self.size-n-1)..-1] : self[-1]
+      end
+
+
+      def pop(n=nil)
+        if n
+          results = []
+          n.times{ results << pop_one }
+          return results
+        else
+          return pop_one
+        end
+      end
+
+
+      def empty?
+        self.size == 0
+      end
+
+      # array aliases into enumerable
+      alias_method :each_index, :each_with_index
+      alias_method :slice, :[]
+      alias_method :values_at, :select
+      alias_method :map, :collect
+
+
+      class << self
+        def define_array_wrapper_method(method_name)
+          define_method(method_name) do |*args, &block|
+            arr = self.to_a
+            result = arr.send(method_name, *args)
+            self.replace(arr)
+            return result if result
+            return block ? block.call : result
+          end
+        end
+        private :define_array_wrapper_method
+
+
+        def define_array_wrapper_with_result_method(method_name)
+          define_method(method_name) do |*args, &block|
+            # result can be an Enumerator, Array, or nil
+            # Enumerator can sometimes be returned if a block is an optional argument and it is not passed in
+            # nil usually specifies that no change was made
+            result = self.to_a.send(method_name, *args, &block)
+            if result
+              new_arr = result.to_a
+              self.replace(new_arr)
+              if result.is_a?(Enumerator)
+                # generate a fresh enum; rewinding the exiting one, in Ruby 2.2, will
+                # reset the enum with the same length, but all the #next calls will
+                # return nil
+                result = new_arr.to_enum
+                # generate a wrapper enum so any changes which occur by a chained
+                # enum can be captured
+                ie = ProxyingEnumerator.new(self, result)
+                result = ie.to_enum
+              end
+            end
+            result
+          end
+        end
+        private :define_array_wrapper_with_result_method
+      end
+
+
+      %w(delete delete_at delete_if shift slice! unshift).each do |method_name|
+        define_array_wrapper_method(method_name)
+      end
+
+
+      %w(collect! compact! fill flatten! insert reverse!
+        rotate! select! shuffle! sort! sort_by! uniq!).each do |method_name|
+        define_array_wrapper_with_result_method(method_name)
+      end
+      alias_method :keep_if, :select!
+      alias_method :map!, :collect!
+      alias_method :reject!, :delete_if
+
+
+      # propagates changes made by user of enumerator back to the original repeated field.
+      # This only applies in cases where the calling function which created the enumerator,
+      # such as #sort!, modifies itself rather than a new array, such as #sort
+      class ProxyingEnumerator < Struct.new(:repeated_field, :external_enumerator)
+        def each(*args, &block)
+          results = []
+          external_enumerator.each_with_index do |val, i|
+            result = yield(val)
+            results << result
+            #nil means no change occured from yield; usually occurs when #to_a is called
+            if result
+              repeated_field[i] = result if result != val
+            end
+          end
+          results
+        end
+      end
 
-      alias_method :size, :length
 
     end
   end
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