Slot with a return value?

[faldzip]

But there is no risk. In Qt documentation it is said that (almost - I think method with variable parameters count - '...' can't) every member function can be a slot. Just place it in public/private/protected slots section in class declaration. So making void returning slots to call non-void returning methods is waste of one more function call, of course unless you don't need returned value.

[squidge]

It's non-standard because a non-void slot will have it's return code ignored. If you wish to call that function normally too, then it makes sense. It's better than having a void slot calling a non-void slot when you are going to ignore the return value anyway - thats just a waste.

[lalesculiviu]

Detailed explanation: I have the function bool fileSave(), which saves the file, and returns true or false (success or not). The user can press button "Save", which is connected to this fileSave. For this, I don't need the bool return value. But I need it for this: when the user wants to Quit my application, I show him a question: "Do you want to save current file". He says "Yes". Then, he may save or hit cancel in the Save file dialog. I need the return code of fileSave(), if it is false, I don't close my application (closeEvent->ignore()).

Yes, you are right that there is an additional function call if I implement a slot void saveFileSlot(), which calls bool fileSave() and ignores the bool return. But remember the 10-90 rule (I mean, you need to only optimize critical code). With current speed, it really does not matter an additional function call for a button press.

I searched the Qt sources and could not find a non-void slot.

Yes, I know current code works. But there is also some other risk: this type of code (non-void slot) may not be tested thoroughly by Qt team.

[squidge]

In the end, its upto you. It's your application.

However, since we know how slots are called, there is really no risk to having a non-void slot.

[wysota]

I sometimes use slots that return values in my code. It's nothing special. As for non-void slots in Qt - I'm almost sure there are some. But they are called using QMetaObject::invokeMethod() because their value is interesting to the caller so it needs to be retrieved.

[lalesculiviu]

OK, thank you, I'll think about it.