get a size of pointer type before converting a type to raise a TypeEr…

…ror when passed invalid argument to Pointer#cast!. fix #1489

bridgesupport.cpp

@@ -883,13 +883,13 @@ rb_pointer_init_type(rb_vm_pointer_t *ptr, VALUE type)
 
     RoxorCore *core = GET_CORE();
 
+    ptr->type_size = core->get_sizeof(type_str);
+    assert(ptr->type_size > 0);
+
     ptr->convert_to_rval =
 	(VALUE (*)(void *))core->gen_to_rval_convertor(type_str);
     ptr->convert_to_ocval =
 	(void (*)(VALUE, void *))core->gen_to_ocval_convertor(type_str);
-
-    ptr->type_size = core->get_sizeof(type_str);
-    assert(ptr->type_size > 0);
 }
 
 extern "C"

spec/macruby/core/pointer_spec.rb

@@ -195,6 +195,13 @@ def coercable_object.to_f; 42.0; end
     pointer2[0].should == NSMakeRect(10, 20, 30, 40)
   end
 
+  it "raises a TypeError when a incompatible object is given into #cast!" do
+    lambda {
+      pointer = Pointer.new('i')
+      pointer.cast!('x')
+    }.should raise_error(TypeError)
+  end
+
   it "of type 'c' can be passed as a C-style char array argument" do
     s = NSString.stringWithString('foo')
     ptr = Pointer.new(:char, 4)