[Development] Converting types in Qt

Olivier Goffart olivier at woboq.com
Thu Jul 17 14:36:22 CEST 2014

On Thursday 17 July 2014 13:33:49 Daniel Teske wrote:
> A equals operator that is not symetric is broken. Such a class cannot be
> reliably used in std nor qt containers. Or do you know which way around,
> QList::contains uses the equals operation?

Note that none of the class which have a member operator== is symmetric.
Most of the class had an operator== as a member in Qt4 but that was a design 
mistake.  New classes should have a friend operator== instead.


qDebug() << (QUrl() == QString());  // true
qDebug() << (QString() == QUrl());  // compilation error

That's because QUrl has a 
 bool QUrl::operator==(const QUrl&);
Instead of
 bool operator==(const QUrl &, const QUrl&);

The later is symmetric, but the former is not.

This is also valid for operator< and related.

(That was just to go a bit more out of topic :-))


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