Add Data class implementation: Simple immutable value object

NEWS.md

@@ -102,6 +102,11 @@ Note that each entry is kept to a minimum, see links for details.
 
 Note: We're only listing outstanding class updates.
 
+* Data
+    * New core class to represent simple immutable value object. The class is
+      similar to `Struct` and partially shares an implementation, but has more
+      lean and strict API. [[Feature #16122]]
+
 * Encoding
     * Encoding#replicate has been deprecated and will be removed in 3.3. [[Feature #18949]]
     * The dummy `Encoding::UTF_16` and `Encoding::UTF_32` encodings no longer
@@ -323,3 +328,4 @@ The following deprecated APIs are removed.
 [Feature #18949]: https://bugs.ruby-lang.org/issues/18949
 [Feature #19008]: https://bugs.ruby-lang.org/issues/19008
 [Feature #19026]: https://bugs.ruby-lang.org/issues/19026
+[Feature #16122]: https://bugs.ruby-lang.org/issues/16122

array.c

@@ -5587,7 +5587,7 @@ ary_recycle_hash(VALUE hash)
  *  Related: Array#difference.
  */
 
-static VALUE
+VALUE
 rb_ary_diff(VALUE ary1, VALUE ary2)
 {
     VALUE ary3;

internal/array.h

@@ -35,6 +35,7 @@ void rb_ary_cancel_sharing(VALUE ary);
 size_t rb_ary_size_as_embedded(VALUE ary);
 void rb_ary_make_embedded(VALUE ary);
 bool rb_ary_embeddable_p(VALUE ary);
+VALUE rb_ary_diff(VALUE ary1, VALUE ary2);
 
 static inline VALUE rb_ary_entry_internal(VALUE ary, long offset);
 static inline bool ARY_PTR_USING_P(VALUE ary);

spec/ruby/core/data/constants_spec.rb

@@ -14,10 +14,22 @@
   end
 end
 
-ruby_version_is '3.0' do
+ruby_version_is '3.0'...'3.2' do
   describe "Data" do
     it "does not exist anymore" do
       Object.should_not have_constant(:Data)
     end
   end
 end
+
+ruby_version_is '3.2' do
+  describe "Data" do
+    it "is a new constant" do
+      Data.superclass.should == Object
+    end
+
+    it "is not deprecated" do
+      -> { Data }.should_not complain
+    end
+  end
+end