Op 20/01/2016 om 06:47 schreef Thiago Macieira:
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.
Indeed.
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
generated.
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.
Where is this qAsConst coming from? When was it introduced? Where is it
documented?
I can't find it in my Qt documentation.
André
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