Implement and untag Enumerator#produce

Author: Lillian Zhang

CHANGELOG.md

@@ -17,6 +17,7 @@ Compatibility:
 * Implement `Enumerable#tally` and `Enumerable#filter_map` (#2144 and #2152, @LillianZ).
 * Implement `Range#minmax`.
 * Pass more `Enumerator::Lazy#uniq` and `Enumerator::Lazy#chunk` specs (#2146, @LillianZ).
+* Implement `Enumerator#produce` (#2160, @zverok)
 
 Performance:
 

spec/tags/core/enumerator/produce_tags.txt

@@ -216,6 +216,19 @@ def +(other)
     Enumerator::Chain.new(self, other)
   end
 
+  def self.produce(initial = nil)
+    # Taken from https://github.com/zverok/enumerator_generate
+    raise ArgumentError, 'No block given' unless block_given?
+    Enumerator.new(Float::INFINITY) do |y|
+      val = initial == nil ? yield() : initial
+
+      loop do
+        y << val
+        val = yield(val)
+      end
+    end
+  end
+
   class Yielder
     def initialize(&block)
       raise LocalJumpError, 'Expected a block to be given' unless block_given?