Revert "Implement Ruby2.7's frozen strings from `Symbol#to_s`"

This feature was reverted from Ruby 2.7.

1 files changed, 4 insertions, 4 deletions

diff --git a/mrbgems/mruby-symbol-ext/mrblib/symbol.rb b/mrbgems/mruby-symbol-ext/mrblib/symbol.rb
index 4b4cf83fe..99fa275d5 100644
--- a/mrbgems/mruby-symbol-ext/mrblib/symbol.rb
+++ b/mrbgems/mruby-symbol-ext/mrblib/symbol.rb
@@ -10,7 +10,7 @@ class Symbol
   # Same as <code>sym.to_s.capitalize.intern</code>.
 
   def capitalize
-    self.to_s.capitalize.to_sym
+    (self.to_s.capitalize! || self).to_sym
   end
 
   ##
@@ -20,7 +20,7 @@ class Symbol
   # Same as <code>sym.to_s.downcase.intern</code>.
 
   def downcase
-    self.to_s.downcase.to_sym
+    (self.to_s.downcase! || self).to_sym
   end
 
   ##
@@ -30,7 +30,7 @@ class Symbol
   # Same as <code>sym.to_s.upcase.intern</code>.
 
   def upcase
-    self.to_s.upcase.to_sym
+    (self.to_s.upcase! || self).to_sym
   end
 
   ##
@@ -41,7 +41,7 @@ class Symbol
 
   def casecmp(other)
     return nil unless other.kind_of?(Symbol)
-    lhs =  self.to_s.upcase
+    lhs =  self.to_s; lhs.upcase!
     rhs = other.to_s.upcase
     lhs <=> rhs
   end