Adding Enumerable#filter_map

[Feature #15323]
Closes: https://github.com/ruby/ruby/pull/2017

enum.c

@@ -452,6 +452,46 @@ enum_find_all(VALUE obj)
     return ary;
 }
 
+static VALUE
+filter_map_i(RB_BLOCK_CALL_FUNC_ARGLIST(i, ary))
+{
+    i = rb_yield_values2(argc, argv);
+
+    if (RTEST(i)) {
+        rb_ary_push(ary, i);
+    }
+
+    return Qnil;
+}
+
+/*
+ *  call-seq:
+ *     enum.filter_map { |obj| block } -> array
+ *     enum.filter_map                 -> an_enumerator
+ *
+ *  Returns a new array containing the truthy results (everything except
+ *  +false+ or +nil+) of running the +block+ for every element in +enum+.
+ *
+ *  If no block is given, an Enumerator is returned instead.
+ *
+ *
+ *     (1..10).filter_map { |i| i * 2 if i.even? } #=> [4, 8, 12, 16, 20]
+ *
+ */
+static VALUE
+enum_filter_map(VALUE obj)
+{
+    VALUE ary;
+
+    RETURN_SIZED_ENUMERATOR(obj, 0, 0, enum_size);
+
+    ary = rb_ary_new();
+    rb_block_call(obj, id_each, 0, 0, filter_map_i, ary);
+
+    return ary;
+}
+
+
 static VALUE
 reject_i(RB_BLOCK_CALL_FUNC_ARGLIST(i, ary))
 {
@@ -4108,6 +4148,7 @@ Init_Enumerable(void)
     rb_define_method(rb_mEnumerable, "find_all", enum_find_all, 0);
     rb_define_method(rb_mEnumerable, "select", enum_find_all, 0);
     rb_define_method(rb_mEnumerable, "filter", enum_find_all, 0);
+    rb_define_method(rb_mEnumerable, "filter_map", enum_filter_map, 0);
     rb_define_method(rb_mEnumerable, "reject", enum_reject, 0);
     rb_define_method(rb_mEnumerable, "collect", enum_collect, 0);
     rb_define_method(rb_mEnumerable, "map", enum_collect, 0);

spec/ruby/core/enumerable/filter_map_spec.rb

@@ -0,0 +1,26 @@
+require_relative '../../spec_helper'
+require_relative 'fixtures/classes'
+
+ruby_version_is '2.7' do
+  describe 'Enumerable#filter_map' do
+    before :each do
+      @numerous = EnumerableSpecs::Numerous.new(*(1..8).to_a)
+    end
+
+    it 'returns an empty array if there are no elements' do
+      EnumerableSpecs::Empty.new.filter_map { true }.should == []
+    end
+
+    it 'returns an array with truthy results of passing each element to block' do
+      @numerous.filter_map { |i| i * 2 if i.even? }.should == [4, 8, 12, 16]
+      @numerous.filter_map { |i| i * 2 }.should == [2, 4, 6, 8, 10, 12, 14, 16]
+      @numerous.filter_map { 0 }.should == [0, 0, 0, 0, 0, 0, 0, 0]
+      @numerous.filter_map { false }.should == []
+      @numerous.filter_map { nil }.should == []
+    end
+
+    it 'returns an enumerator when no block given' do
+      @numerous.filter_map.should be_an_instance_of(Enumerator)
+    end
+  end
+end

test/ruby/test_enum.rb

@@ -1135,4 +1135,14 @@ class TestEnumerable < Test::Unit::TestCase
     end
     assert_equal [1, 2, 3, 4, 5], (1..5).sort_by{|e| klass.new e}
   end
+
+  def test_filter_map
+    @obj = (1..8).to_a
+    assert_equal([4, 8, 12, 16], @obj.filter_map { |i| i * 2 if i.even? })
+    assert_equal([2, 4, 6, 8, 10, 12, 14, 16], @obj.filter_map { |i| i * 2 })
+    assert_equal([0, 0, 0, 0, 0, 0, 0, 0], @obj.filter_map { 0 })
+    assert_equal([], @obj.filter_map { false })
+    assert_equal([], @obj.filter_map { nil })
+    assert_instance_of(Enumerator, @obj.filter_map)
+  end
 end

test/ruby/test_enumerator.rb

@@ -542,7 +542,7 @@ class TestEnumerator < Test::Unit::TestCase
 
   def test_size_for_enum_created_from_enumerable
     %i[find_all reject map flat_map partition group_by sort_by min_by max_by
-      minmax_by each_with_index reverse_each each_entry].each do |method|
+      minmax_by each_with_index reverse_each each_entry filter_map].each do |method|
       assert_equal nil, @obj.send(method).size
       assert_equal 42, @sized.send(method).size
     end