string interpolation (#{foo}) does stringify implicitly; no need to call #to_s

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

@@ -20,7 +20,7 @@ class Array
   end
 
   def -(elem)
-    raise TypeError, "can't convert #{elem.class.to_s} into Array" unless elem.class == Array
+    raise TypeError, "can't convert #{elem.class} into Array" unless elem.class == Array
 
     hash = {}
     array = []
@@ -30,14 +30,14 @@ class Array
   end
 
   def |(elem)
-    raise TypeError, "can't convert #{elem.class.to_s} into Array" unless elem.class == Array
+    raise TypeError, "can't convert #{elem.class} into Array" unless elem.class == Array
 
     ary = self + elem
     ary.uniq! or ary
   end
 
   def &(elem)
-    raise TypeError, "can't convert #{elem.class.to_s} into Array" unless elem.class == Array
+    raise TypeError, "can't convert #{elem.class} into Array" unless elem.class == Array
 
     hash = {}
     array = []

src/object.c

@@ -305,9 +305,7 @@ convert_type(mrb_state *mrb, mrb_value val, const char *tname, const char *metho
   m = mrb_intern(mrb, method);
   if (!mrb_respond_to(mrb, val, m)) {
     if (raise) {
-      const char *cname = mrb_obj_classname(mrb, val);
-      mrb_raisef(mrb, E_TYPE_ERROR, "can't convert %S into %S",
-                 mrb_str_new_cstr(mrb, cname), mrb_str_new_cstr(mrb, tname));
+      mrb_raisef(mrb, E_TYPE_ERROR, "can't convert %S into %S", val, mrb_str_new_cstr(mrb, tname));
       return mrb_nil_value();
     }
     else {