[Development] QTextStream::readLine(0) is an ambiguous overload in 5.5

Andre Somers andre at familiesomers.nl
Sun May 17 14:30:16 CEST 2015

On 13-5-2015 2:44, Thiago Macieira wrote:
> On Wednesday 13 May 2015 02:34:28 Jan Kundrát wrote:
>> Hi,
>> this commit [1] added a new overload to QTextStream::readLine. As a result
>> of that, calling stream.readLine(0) is now ambiguous:
>>      QString readLine(qint64 maxlen = 0);
>>      bool readLine(QString *line, qint64 maxlen = 0);
>> While I can easily fix this in the caller (Konsole in this case), I'm
>> wodnering whether this effect was understood at the time the change was
>> merged. IMHO it's a bit more user-friendly to preserve source compatibility
>> by removing the default value in the newly added overload.
>> Should I send such a patch?
> Why write readLine(0) when it's the same as readLine() ? readLine(0) seems to
> me that it's asking for a line of at most zero bytes -- we should have had
> this argument default to -1 to indicate maximum length, not 0.
> Removing the default argument for the new overload will make it worse, by
> making people have to write the zero when they mean unlimited. I don't like
> that. The two options I will consider are:
> a) do nothing, accept and document the source incompatibility
> b) modify differently so that the new API isn't ambiguous but doesn't require
> people to write 0 either.
In the spirit of option b), would it be an option to have the method 
take a QString& instead of a QString*? That would resolve the ambiguity. 
It also makes it clear that it makes little sense to call the method 
without an actual QString to store the results in.


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