[Development] Fw: Important recent changes in QList/QString/QByteArray

Jaroslaw Kobus Jaroslaw.Kobus at qt.io
Thu Sep 3 09:40:29 CEST 2020

> ________________________________________
> From: Development <development-bounces at qt-project.org> on behalf of Giuseppe D'Angelo via Development <development at qt-project.org>
> Sent: Wednesday, September 2, 2020 9:37 PM
> To: Andrei Golubev; development at qt-project.org; Ville Voutilainen
> Subject: Re: [Development] Important recent changes in  QList/QString/QByteArray
> On 02/09/2020 21:18, Andrei Golubev wrote:
> > Also not sure whether it is an implementation detail or the behavior
> > that should always be anticipated.
> People build performance sensitive code assuming the cost of certain
> operations -- like, assuming that erasing elements from a vector never
> reallocates it; and that the only operation that sheds capacity is
> squeeze(), everything else (incl. clear(), incl. resize(0)) keeps the
> capacity (*). We should stop backstabbing them...

People sometimes care about memory consumption, too. If user's object
contains a vector consisting of exactly one element, he may be surprised
that it still consumes a place for one million elements, just because one
minute ago he removed 999.999 items. If he is creating hundreds
of such objects sequentially, his app may not run at all (however, will perform very well).


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