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I recently posted a question about the overhead of QObject in typical usage scenarios, but unfortunately the question got closed as a duplicate of another question that didn't technically answer the question.
What is worse, the hasty "Samaritans" who politely rushed to close my question interrupted the answer I was just finishing typing after running a few tests. Since I can no longer post my findings in my original question, I'll post it here so it is available to others who might need that information.
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There are several reasons why a QObject can't be copied. The two biggest reasons are: QObjects usually communicate with each other using the signals and slots mechanism. It's unclear whether the connected signals and/or slots should be transferred over to the copy.
QObject is the heart of the Qt Object Model. The central feature in this model is a very powerful mechanism for seamless object communication called signals and slots. You can connect a signal to a slot with connect() and destroy the connection with disconnect().
The Q_OBJECT macro is used to enable meta-object features when declared within a class definition. The Meta-Object Compiler ( moc ) will read the class definitions with the declared Q_OBJECT macro and produce the meta-object code.
A lot of people have hinted at QObject being heavy, but without any clarity on how heavy is it exactly. So I did some measurements, not very accurate, all values are approximate.
Those numbers should take into account I am using a 64 bit Qt build.
So, in conclusion, the overhead of QObject is quite significant indeed. Nothing to sneeze at or overuse.
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