Promise.zip execution changes

lib/concurrent/promise.rb

@@ -383,11 +383,24 @@ def flat_map(&block)
     # Builds a promise that produces the result of promises in an Array
     # and fails if any of them fails.
     #
-    # @param [Array<Promise>] promises
+    # @overload zip(*promises)
+    #   @param [Array<Promise>] promises
+    #
+    # @overload zip(*promises, opts)
+    #   @param [Array<Promise>] promises
+    #   @param [Hash] opts the configuration options
+    #   @option opts [Executor] :executor (ImmediateExecutor.new) when set use the given `Executor` instance.
+    #   @option opts [Boolean] :execute (true) execute promise before returning
     #
     # @return [Promise<Array>]
     def self.zip(*promises)
-      zero = fulfill([], executor: ImmediateExecutor.new)
+      opts = promises.last.is_a?(::Hash) ? promises.pop.dup : {}
+      opts[:executor] ||= ImmediateExecutor.new
+      zero = if !opts.key?(:execute) || opts.delete(:execute)
+        fulfill([], opts)
+      else
+        Promise.new(opts) { [] }
+      end
 
       promises.reduce(zero) do |p1, p2|
         p1.flat_map do |results|
@@ -401,7 +414,14 @@ def self.zip(*promises)
     # Builds a promise that produces the result of self and others in an Array
     # and fails if any of them fails.
     #
-    # @param [Array<Promise>] others
+    # @overload zip(*promises)
+    #   @param [Array<Promise>] others
+    #
+    # @overload zip(*promises, opts)
+    #   @param [Array<Promise>] others
+    #   @param [Hash] opts the configuration options
+    #   @option opts [Executor] :executor (ImmediateExecutor.new) when set use the given `Executor` instance.
+    #   @option opts [Boolean] :execute (true) execute promise before returning
     #
     # @return [Promise<Array>]
     def zip(*others)

spec/concurrent/promise_spec.rb

@@ -357,6 +357,32 @@ def get_ivar_from_args(opts)
       let(:promise2) { Promise.new(executor: :immediate) { 2 } }
       let(:promise3) { Promise.new(executor: :immediate) { [3] } }
 
+      it 'executes the returned Promise by default' do
+        composite = promise1.zip(promise2, promise3)
+
+        expect(composite).to be_fulfilled
+      end
+
+      it 'executes the returned Promise when execute is true' do
+        composite = promise1.zip(promise2, promise3, execute: true)
+
+        expect(composite).to be_fulfilled
+      end
+
+      it 'does not execute the returned Promise when execute is false' do
+        composite = promise1.zip(promise2, promise3, execute: false)
+
+        expect(composite).to be_unscheduled
+      end
+
+      it 'allows setting executor for Promise chain' do
+        new_executor = Concurrent::SingleThreadExecutor.new
+        promise = promise1.zip(promise2, promise3, executor: new_executor)
+
+        promise = promise.instance_variable_get(:@parent) until promise.send(:root?)
+        expect(promise.instance_variable_get(:@executor)).to be(new_executor)
+      end
+
       it 'yields the results as an array' do
         composite = promise1.zip(promise2, promise3).execute.wait
 
@@ -375,6 +401,32 @@ def get_ivar_from_args(opts)
       let(:promise2) { Promise.new(executor: :immediate) { 2 } }
       let(:promise3) { Promise.new(executor: :immediate) { [3] } }
 
+      it 'executes the returned Promise by default' do
+        composite = Promise.zip(promise1, promise2, promise3)
+
+        expect(composite).to be_fulfilled
+      end
+
+      it 'executes the returned Promise when execute is true' do
+        composite = Promise.zip(promise1, promise2, promise3, execute: true)
+
+        expect(composite).to be_fulfilled
+      end
+
+      it 'does not execute the returned Promise when execute is false' do
+        composite = Promise.zip(promise1, promise2, promise3, execute: false)
+
+        expect(composite).to be_unscheduled
+      end
+
+      it 'allows setting executor for Promise chain' do
+        new_executor = Concurrent::SingleThreadExecutor.new
+        promise = Promise.zip(promise1, promise2, promise3, executor: new_executor)
+
+        promise = promise.instance_variable_get(:@parent) until promise.send(:root?)
+        expect(promise.instance_variable_get(:@executor)).to be(new_executor)
+      end
+
       it 'yields the results as an array' do
         composite = Promise.zip(promise1, promise2, promise3).execute.wait