[Development] QOptional

[Harri Porten]

On Thu, 21 Aug 2014, Julien Blanc wrote:

> There are two strong arguments in favor of optional :
> - real life tends to show that the optional &ok parameter is often
> missed in context it should not, leading to hard to find bugs. People
> just write
>
> const int value= string.toInt();
>
> optional makes it more obvious for the lazy user that this can fail in
> some contexts.

Unfortunately, I have some doubts about that :}

> It can also assert in debug if dereferenced, for example,
> making bug finding easier.
>
> - optional is much more friendly to static verification than &ok
> (dependancy between variables is a mess to check).
>
> Still, the issue about the semantic of “if(value)” when value == 0 /
> false is still a concern (and one of the reason optional is not part of
> the standard iirc)

Others have said that it's too late to change toInt() and QSql. But how 
about new code including that written by application developers? I 
personally found myself repeating an implementation of "is valid" in 
custom types to signal lack of a proper result. To avoid this repetition 
(which uglifies the type implementation) I can see QOptional being useful.

Harri.