allow disabling Struct class

include/mrbconf.h

@@ -18,6 +18,7 @@
 #undef DISABLE_KERNEL_SPRINTF	/* Kernel.sprintf method */
 #undef DISABLE_MATH		/* Math functions */
 #undef DISABLE_TIME		/* Time class */
+#undef DISABLE_STRUCT		/* Struct class */
 
 #undef  HAVE_UNISTD_H /* WINDOWS */
 #define HAVE_UNISTD_H /* LINUX */
@@ -46,6 +47,9 @@ typedef intptr_t mrb_sym;
 #ifndef DISABLE_TIME
 #define ENABLE_TIME
 #endif
+#ifndef DISABLE_STRUCT
+#define ENABLE_STRUCT
+#endif
 
 #ifndef FALSE
 # define FALSE 0

src/init.c

@@ -49,7 +49,9 @@ mrb_init_core(mrb_state *mrb)
   mrb_init_hash(mrb);
   mrb_init_numeric(mrb);
   mrb_init_range(mrb);
+#ifdef ENABLE_STRUCT
   mrb_init_struct(mrb);
+#endif
   mrb_init_gc(mrb);
 #ifdef ENABLE_REGEXP
   mrb_init_regexp(mrb);

src/struct.c

@@ -5,6 +5,7 @@
 */
 
 #include "mruby.h"
+#ifdef ENABLE_STRUCT
 #include <string.h>
 #include "error.h"
 #include "mruby/struct.h"
@@ -793,3 +794,4 @@ mrb_init_struct(mrb_state *mrb)
   mrb_define_method(mrb, st,       "eql?",            mrb_struct_eql,         ARGS_REQ(1)); /* 15.2.18.4.12(x)  */
 
 }
+#endif	/* ENABLE_STRUCT */