Question about QofIdType assertion in QofCollection

John Ralls jralls at
Mon Dec 29 12:08:01 EST 2014

> On Dec 29, 2014, at 7:32 AM, Chenxiong Qi <qcxhome at> wrote:
> On Mon, Dec 29, 2014 at 8:22 PM, Derek Atkins <derek at> wrote:
>> Because it's a constant.
> Thanks!
> In following scenario, a QofInstance cannot be added into a QofCollection
> QofIdType type = "some type";
> QofInstance inst = g_object_new (QOF_TYPE_INSTANCE, NULL);
> inst->e_type = type;
> QofCollection coll = qof_collection_new (type);
> qof_collection_add_entity (coll, inst);
> The last call will always fail, because coll's e_type has different
> address with the original variable type due to invocation of
> static_cast<QofIdType>

Which is a good thing in this case, because otherwise it would crash when you try to test inst->e_type later, after the function has exited and type is no longer valid. It's not the static_cast<QofIdType>() that changes coll->e_type, it's CACHE_INSERT(type), which does a string copy so that the type doesn't go out of scope. 

You can either preempt it with
  QofIdType type = STRING_CACHE("some type");
Once the string is in the cache, all other calls to STRING_CACHE() will return the same pointer, or you could create the collection first and then 
  inst->e_type = qof_collection_get_type (coll);

Your C++ implementation won't work that way, of course: You'll use templates to enforce proper type safety instead of horrid string hacks. Right?

John Ralls

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