[Development] Use of Standard Library containers in Qt source code

[Thiago Macieira]

Premises not under discussion:

	Qt source code is product and meant to be read by our users
	Qt source code must be clean and readable

The above is not up for debate.

For some time now, we've had a flurry of changes to Qt source code that uses 
the Standard Library's containers and algorithms, in the name of performance 
and often code size gains.

I'm not disputing that there is a gain. But I am wondering about the trade-off 
we're making with regards to readability. For example, I was just reviewing 
this code:

    if (d->currentReadChannel >= d->readHeaders.size()
        || d->readHeaders[d->currentReadChannel].empty()) {
        Q_ASSERT(d->buffer.isEmpty());

The use of the Standard Library member "empty" is highly confusing at first 
sight because it does not follow the Qt naming guidelines. It's even more 
confusing because the next line has "isEmpty". When I read this code, I had to 
wonder if that "empty" was a verb in the imperative, meaning the author was 
trying to remove all elements from the container. 

I had to look up the definition of readHeaders in the review and note that it 
was a std::deque, not a Qt container.

What do we do?

Option 1:
Not use Standard Library containers, just use the Qt containers as they exist.

Option 2:
Create new Qt containers to have the same complexity as Standard Library 
containers, but following the Qt naming conventions. Possibly with implicit 
sharing.

Option 3:
Create Qt API wrappers for those containers like std::deque, adding only a few 
inline functions to match the Qt-style API where the Standard Library API 
deviates. Examples are:
	empty		->	isEmpty
	push_back	->	append
	front		-> 	first
	pop_front	->	takeFirst
	cbegin		->	constBegin
	cfind		->	constFind

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center