[EXPERIMENTAL] Make NilClass#to_s, TrueClass#to_s and FalseClass#to_s return a frozen String

    * Always the same frozen String for each of these values.
    * Avoids extra allocations whenever calling these 3 methods.
    * See [Feature #16150]

3 files changed, 30 insertions, 0 deletions

diff --git a/spec/ruby/core/false/to_s_spec.rb b/spec/ruby/core/false/to_s_spec.rb
index 40853da88b..c996d87000 100644
--- a/spec/ruby/core/false/to_s_spec.rb
+++ b/spec/ruby/core/false/to_s_spec.rb
@@ -4,4 +4,14 @@ describe "FalseClass#to_s" do
   it "returns the string 'false'" do
     false.to_s.should == "false"
   end
+
+  ruby_version_is "2.7" do
+    it "returns a frozen string" do
+      false.to_s.frozen?.should == true
+    end
+
+    it "always returns the same string" do
+      false.to_s.should equal(false.to_s)
+    end
+  end
 end
diff --git a/spec/ruby/core/nil/to_s_spec.rb b/spec/ruby/core/nil/to_s_spec.rb
index c7a18e2527..4b61f589f7 100644
--- a/spec/ruby/core/nil/to_s_spec.rb
+++ b/spec/ruby/core/nil/to_s_spec.rb
@@ -4,4 +4,14 @@ describe "NilClass#to_s" do
   it "returns the string ''" do
     nil.to_s.should == ""
   end
+
+  ruby_version_is "2.7" do
+    it "returns a frozen string" do
+      nil.to_s.frozen?.should == true
+    end
+
+    it "always returns the same string" do
+      nil.to_s.should equal(nil.to_s)
+    end
+  end
 end
diff --git a/spec/ruby/core/true/to_s_spec.rb b/spec/ruby/core/true/to_s_spec.rb
index 30ca354b0c..68b0052c5d 100644
--- a/spec/ruby/core/true/to_s_spec.rb
+++ b/spec/ruby/core/true/to_s_spec.rb
@@ -4,4 +4,14 @@ describe "TrueClass#to_s" do
   it "returns the string 'true'" do
     true.to_s.should == "true"
   end
+
+  ruby_version_is "2.7" do
+    it "returns a frozen string" do
+      true.to_s.frozen?.should == true
+    end
+
+    it "always returns the same string" do
+      true.to_s.should equal(true.to_s)
+    end
+  end
 end