> On Dec 30, 2014, at 1:40 AM, Chenxiong Qi <qcxh...@gmail.com> wrote:
>
> On Tue, Dec 30, 2014 at 1:08 AM, John Ralls <jra...@ceridwen.us> wrote:
>>
>>> On Dec 29, 2014, at 7:32 AM, Chenxiong Qi <qcxh...@gmail.com> wrote:
>>>
>>> On Mon, Dec 29, 2014 at 8:22 PM, Derek Atkins <de...@ihtfp.com> 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 is no longer valid.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);
>>
>
> Thanks Mr. Ralls. I'm writing unit tests for QofCollection C
> interfaces, that allows me to know much details of QofCollection and
> QofInstance. Another question is about qof_collection_add_entity.
> Sorry for not starting a separate thread for this, I think they are
> same things of a kind to QofCollection.
>
> qof_collection_add_entity does not set collection attribute of a
> QofInstance once it is added, but qof_collection_insert_entity does
> this. This confuses me. By going through the code, I think both of
> them should have same behavior. Am I right, or something I missed and
> understand incorrectly?
Qi,
You have to look at the usage of each call. qof_collection_insert_entity is
used by QofInstance to register itself with the book and stores a backlink to
the collection so that given an instance the collection can be easily retrieved
and searched for something else, while qof_collection_add_entity is used by
gncInvoice for a private collection. In the latter case over-writing the
collection pointer on the instance would destroy the back link to the book’s
collection.
The backlink is redundant since every instance also has a pointer to its book
and the book owns the collections in question, so when reimplementing it I
wouldn’t include the collection link, but the current design needs it.
When searching for a function name remember to search for scheme wrappers,
where underscores are replaced with hyphens. E.g. `grep -r
gnc[-_]get[-_]current[-_]book src`.
Regards,
John Ralls
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