[GR-20446] Implement Enumerator::Lazy#filter_map

PullRequest: truffleruby/2667

Author: bjfish

CHANGELOG.md

@@ -29,6 +29,7 @@ Compatibility:
 * Update `File.basename` to return new `String` instances (#2343).
 * Allow `Fiber#raise` after `Fiber#transfer` like Ruby 3.0 (#2342).
 * Fix `ObjectSpace._id2ref` for Symbols and frozen String literals (#2358).
+* Implemented `Enumerator::Lazy#filter_map` (#2356).
 
 Performance:
 

spec/ruby/core/enumerator/lazy/filter_map_spec.rb

@@ -0,0 +1,16 @@
+# -*- encoding: us-ascii -*-
+
+require_relative '../../../spec_helper'
+require_relative 'fixtures/classes'
+
+ruby_version_is "2.7" do
+  describe "Enumerator::Lazy#filter_map" do
+    it "maps only truthy results" do
+      (1..Float::INFINITY).lazy.filter_map { |i| i if i.odd? }.first(4).should == [1, 3, 5, 7]
+    end
+
+    it "does not map nil results" do
+      (1..Float::INFINITY).lazy.filter_map { |i| i.odd? ? i : nil }.first(4).should == [1, 3, 5, 7]
+    end
+  end
+end

spec/tags/truffle/methods_tags.txt

@@ -57,7 +57,6 @@ fails:Public methods on TracePoint should include parameters
 fails:Public methods on TracePoint should include raised_exception
 fails:Public methods on TracePoint should include return_value
 fails:Public methods on ENV.singleton_class should include freeze
-fails:Public methods on Enumerator::Lazy should include filter_map
 fails:Public methods on Enumerator::Lazy should include with_index
 fails:Public methods on IO should include set_encoding_by_bom
 fails:Public methods on BasicSocket should include read_nonblock

src/main/ruby/truffleruby/core/enumerator.rb

@@ -393,6 +393,15 @@ def drop_while
       end
     end
 
+    def filter_map
+      raise ArgumentError, 'Lazy#filter_map requires a block' unless block_given?
+
+      Lazy.new(self, enumerator_size) do |yielder, *args|
+        result = yield(*args)
+        yielder.yield result if result
+      end
+    end
+
     def select
       raise ArgumentError, 'Lazy#{select,find_all} requires a block' unless block_given?