[EXPERIMENTAL] Make Symbol#to_s return a frozen String

* Always the same frozen String for a given Symbol.
* Avoids extra allocations whenever calling Symbol#to_s.
* See [Feature #16150]

1 files changed, 17 insertions, 0 deletions

diff --git a/spec/ruby/core/symbol/shared/id2name.rb b/spec/ruby/core/symbol/shared/id2name.rb
index 47f97bd332..a0e190a680 100644
--- a/spec/ruby/core/symbol/shared/id2name.rb
+++ b/spec/ruby/core/symbol/shared/id2name.rb
@@ -6,4 +6,21 @@ describe :symbol_id2name, shared: true do
     :@ruby.send(@method).should == "@ruby"
     :@@ruby.send(@method).should == "@@ruby"
   end
+
+  ruby_version_is "2.7" do
+    it "returns a frozen String" do
+      :my_symbol.to_s.frozen?.should == true
+      :"dynamic symbol #{6 * 7}".to_s.frozen?.should == true
+    end
+
+    it "always returns the same String for a given Symbol" do
+      s1 = :my_symbol.to_s
+      s2 = :my_symbol.to_s
+      s1.should equal(s2)
+
+      s1 = :"dynamic symbol #{6 * 7}".to_s
+      s2 = :"dynamic symbol #{2 * 3 * 7}".to_s
+      s1.should equal(s2)
+    end
+  end
 end