Add `{String,Symbol}#casecmp?`; CRuby2.4

mrbgems/mruby-string-ext/mrblib/string.rb

@@ -144,7 +144,20 @@ class String
   def casecmp(str)
     self.downcase <=> str.to_str.downcase
   rescue NoMethodError
-    raise TypeError, "no implicit conversion of #{str.class} into String"
+    nil
+  end
+
+  ##
+  # call-seq:
+  #   str.casecmp?(other)  -> true, false, or nil
+  #
+  # Returns true if str and other_str are equal after case folding,
+  # false if they are not equal, and nil if other_str is not a string.
+
+  def casecmp?(str)
+    c = self.casecmp(str)
+    return nil if c.nil?
+    return c == 0
   end
 
   def partition(sep)

mrbgems/mruby-symbol-ext/mrblib/symbol.rb

@@ -48,10 +48,23 @@ class Symbol
   def casecmp(other)
     return nil unless other.kind_of?(Symbol)
     lhs =  self.to_s; lhs.upcase!
-    rhs = other.to_s; rhs.upcase!
+    rhs = other.to_s.upcase
     lhs <=> rhs
   end
 
+  ##
+  # call-seq:
+  #   sym.casecmp?(other)  -> true, false, or nil
+  #
+  # Returns true if sym and other_sym are equal after case folding,
+  # false if they are not equal, and nil if other_sym is not a string.
+
+  def casecmp?(sym)
+    c = self.casecmp(sym)
+    return nil if c.nil?
+    return c == 0
+  end
+
   #
   # call-seq:
   #   sym.empty?   -> true or false