[Development] qMoveToConst helper for rvalue references to movable Qt containers?

[Lars Knoll]

On 27 Oct 2018, at 19:29, André Pönitz <apoenitz at t-online.de<mailto:apoenitz at t-online.de>> wrote:

On Sat, Oct 27, 2018 at 04:33:30PM +0100, Sérgio Martins wrote:
On Sat, Oct 20, 2018 at 1:44 PM Elvis Stansvik <elvstone at gmail.com<mailto:elvstone at gmail.com>> wrote:

Hi all (first post),

Welcome :)

In Qt 5.7+ there's qAsConst, an std::as_const implementation for those
who are not on C++17 yet, which is convenient for iterating over Qt
containers using range-based for loops without causing a detach.

For good reasons there's no version of qAsConst that takes an rvalue
reference, so you can't do e.g. for (auto foo :
qAsConst(returnsQtContainer())  { ... }. Instead you must do const
auto stuff = returnsQtContainer(); for (auto foo : stuff) { ... }.

Should we instead just encourage people to make returnsQtContainer()
return a const container ?

This is actually a route we recently took in some cases in Qt Creator's
code base.

That might actually make sense. Calling a non const method on the returned temporary object is usually a mistake anyway. And the copy/move assignment to a variable will work with the const object.

Cheers,
Lars

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