Need explicit cast for C++
MODIFY
include/mruby/data.h
include/mruby/data.h
@@ -41,7 +41,7 @@ MRB_API struct RData *mrb_data_object_alloc(mrb_state *mrb, struct RClass* klass
#define Data_Make_Struct(mrb,klass,strct,type,sval,data_obj) do { \
(data_obj) = Data_Wrap_Struct(mrb,klass,type,NULL);\
- (sval) = mrb_malloc(mrb, sizeof(strct)); \
+ (sval) = (strct *)mrb_malloc(mrb, sizeof(strct)); \
{ static const strct zero = { 0 }; *(sval) = zero; };\
(data_obj)->data = (sval);\
} while (0)

Need explicit cast for C++