Support freeze in `Struct`.

mrbgems/mruby-struct/src/struct.c

@@ -84,6 +84,16 @@ mrb_struct_s_members_m(mrb_state *mrb, mrb_value klass)
   return ary;
 }
 
+static void
+mrb_struct_modify(mrb_state *mrb, mrb_value strct)
+{
+  if (MRB_FROZEN_P(mrb_basic_ptr(strct))) {
+    mrb_raise(mrb, E_RUNTIME_ERROR, "can't modify frozen struct");
+  }
+
+  mrb_write_barrier(mrb, mrb_basic_ptr(strct));
+}
+
 /* 15.2.18.4.6  */
 /*
  *  call-seq:
@@ -448,8 +458,8 @@ mrb_struct_aset_sym(mrb_state *mrb, mrb_value s, mrb_sym id, mrb_value val)
   ptr_members = RARRAY_PTR(members);
   for (i=0; i<len; i++) {
     if (mrb_symbol(ptr_members[i]) == id) {
+      mrb_struct_modify(mrb, s);
       ptr[i] = val;
-      mrb_write_barrier(mrb, (struct RBasic*)mrb_ptr(s));
       return val;
     }
   }
@@ -512,7 +522,7 @@ mrb_struct_aset(mrb_state *mrb, mrb_value s)
                "offset %S too large for struct(size:%S)",
                mrb_fixnum_value(i), mrb_fixnum_value(RSTRUCT_LEN(s)));
   }
-  mrb_write_barrier(mrb, (struct RBasic*)mrb_ptr(s));
+  mrb_struct_modify(mrb, s);
   return RSTRUCT_PTR(s)[i] = val;
 }
 

mrbgems/mruby-struct/test/struct.rb

@@ -197,3 +197,16 @@ assert("Struct.new generates subclass of Struct") do
     Struct = original_struct
   end
 end
+
+assert 'Struct#freeze' do
+  c = Struct.new :m
+
+  o = c.new
+  o.m = :test
+  assert_equal :test, o.m
+
+  o.freeze
+  assert_raise(RuntimeError) { o.m = :modify }
+  assert_raise(RuntimeError) { o[:m] = :modify }
+  assert_equal :test, o.m
+end