[Development] A QStringList puzzle for Monday

[Marc Mutz]

On 17.03.25 20:09, Jøger Hansegård via Development wrote:
[...]
> I agree that it would be nice to have a compiler error but given that QStringList behaves the same way as std::vector, I am not sure it is a bug.

For the specific case of QList, we could take first and last by 
reference, preventing the decay of the argument to pointers, and thus to 
something that looks like iterators. But that's shotgun surgery. 
Everywhere else (incl. STL) iterators are passed by value, and make 
arguments decay.

The solution, as others have pointed out, is simple: don't use C string 
literals to initialize QStrings. Define QT_NO_CAST_FROM_ASCII (and 
_TO_ASCII, _FROM_BYTEARRAY, to fix two other gotchas), and use 
Qt::StringLiteral UDLs, which make QT_NO_CAST_FROM_ASCII bearable for 
the first time in Qt's history.

Also, get into the habit of using {} instead of () unless you need to 
tie-break between an initializer_list constructor and 
non-initializer_list one. It also prevents narrowing.

Daunting for an existing project to implement, but trivial if you just 
start out.

The action point for Qt itself is to avoid APIs that depend too much on 
implicit conversion and overloading. Prefer named constructors 
(QList::fromRange), and explicit function names 
(appendString()/appendByteArray() instead of 
append(QString)/append(QByteArray)). Make ctors and conversion operator explicit.

Thanks,
Marc

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Marc Mutz <marc.mutz at qt.io> (he/his)
Principal Software Engineer

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