Implement write barriers for Fiddle::Pointer (#127)

Save from having to mark them on every minor.
Co-authored-by: Jean Boussier <jean.boussier@gmail.com>

Author: casperisfine

ext/fiddle/pointer.c

@@ -88,8 +88,13 @@ fiddle_ptr_memsize(const void *ptr)
 }
 
 staticconstrb_data_type_tfiddle_ptr_data_type= {
-"fiddle/pointer",
- {fiddle_ptr_mark, fiddle_ptr_free, fiddle_ptr_memsize,},
+ .wrap_struct_name="fiddle/pointer",
+ .function= {
+ .dmark=fiddle_ptr_mark,
+ .dfree=fiddle_ptr_free,
+ .dsize=fiddle_ptr_memsize,
+ },
+ .flags=RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_WB_PROTECTED
 };
 
 #ifdefHAVE_RUBY_MEMORY_VIEW_H
@@ -135,8 +140,8 @@ rb_fiddle_ptr_new2(VALUE klass, void *ptr, long size, freefunc_t func, VALUE wra
 data->free=func;
 data->freed= false;
 data->size=size;
-data->wrap[0]=wrap0;
-data->wrap[1]=wrap1;
+RB_OBJ_WRITE(val, &data->wrap[0], wrap0);
+RB_OBJ_WRITE(val, &data->wrap[1], wrap1);
 
 returnval;
 }
@@ -235,8 +240,8 @@ rb_fiddle_ptr_initialize(int argc, VALUE argv[], VALUE self)
 /* Free previous memory. Use of inappropriate initialize may cause SEGV. */
  (*(data->free))(data->ptr);
 	}
-data->wrap[0]=wrap;
-data->wrap[1]=funcwrap;
+RB_OBJ_WRITE(self, &data->wrap[0], wrap);
+RB_OBJ_WRITE(self, &data->wrap[1], funcwrap);
 data->ptr=p;
 data->size=s;
 data->free=f;
@@ -314,7 +319,7 @@ rb_fiddle_ptr_s_malloc(int argc, VALUE argv[], VALUE klass)
  }
 
 obj=rb_fiddle_ptr_malloc(klass, s,f);
-if (wrap) RPTR_DATA(obj)->wrap[1]=wrap;
+if (wrap) RB_OBJ_WRITE(obj, &RPTR_DATA(obj)->wrap[1], wrap);
 
 if (rb_block_given_p()) {
 if (!f) {
@@ -795,7 +800,7 @@ rb_fiddle_ptr_s_to_ptr(VALUE self, VALUE val)
 if (num==val) wrap=0;
 ptr=rb_fiddle_ptr_new(NUM2PTR(num), 0, NULL);
  }
-if (wrap) RPTR_DATA(ptr)->wrap[0]=wrap;
+if (wrap) RB_OBJ_WRITE(ptr, &RPTR_DATA(ptr)->wrap[0], wrap);
 returnptr;
 }