[Development] QStringLiteral vs QLatin1String , foreach vs for range

Thiago Macieira thiago.macieira at intel.com
Wed Jan 20 06:47:38 CET 2016

On Wednesday 20 January 2016 05:20:36 Kevin Kofler wrote:
> Thiago Macieira wrote:
> > foreach copies; ranged for doesn't.
> … unless you try to use it on a non-const Qt container with usage count >1,
> then it will even deep-copy (detach) it! (I know you know this, but you
> should warn people about it.) So you need to be very careful about what you
> pass to ranged for.


But his is the argument that convinced me: with foreach and Qt containers, you 
usually get the runtime performance you want, but it costs in dead code since 
the deep-copy code will be present (at least until we can get rid of the 
unsharable flag). With ranged for plus qAsConst, there's no copy code 

So instead of:

	foreach (auto x, container)

You'll write:

	for (auto x : qAsConst(container))

or if you know it's already const, you can skip the qAsConst part.

This is no more and no less readable, but is more explicit about what it does.
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center

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