4 ms·

Or you can use std::function. It's fractionally less efficient but much easier to understand and doesn't all have to go in the header (and only needs C++11):

Or you can use std::function. It's fractionally less efficient but much easier to understand and doesn't all have to go in the header (and only needs C++11): void addListener(std::function<int(Button*)> cb)

jcelerier 8y ago
> fractionally less efficient std::function can potentially allocate memory and hides stuff behind a vtable, e.g. two indirections. That's not what I would call "frationally less efficient".
- htfy96 8y ago
  Personally I doubted about the overhead on nowadays machines. I guess a Electron app with a button definitely goes over more abstraction than several indirection when it is clicked. Should we really care about these overhead, at least on desktop platform?
- quietbritishjim 8y ago
  Perhaps "fractional" is the wrong word because has a literal meaning which probably isn't true if you compare calling a std::function vs calling a function directly within a template (although you still need to call that template from somewhere so you'll probably end up with at least one indirection, but I digress). But as a fraction of your application's overall runtime, in almost cases it's going to be an absolutely insignificant fraction, like less than a millionth of the runtime. This is certainly true if you're writing a GUI or a network-based server process. For it to be noticeable you'd have to be calling the callback in an extraordinarily tight loop, where the actual function does very little (less than a few pointer indirections!). Put another way, avoiding std::function is a classic case of premature optimisation.
  - jcelerier 8y ago
    > This is certainly true if you're writing a GUI or a network-based server process. But are you writing those in C++ ? C++ is used exactly where you have those tight loops. Execution engines, VMs and interpreters... Besides, as soon as you want to have some real-time behaviour you can't have any call to malloc since it may make performance much less deterministic due to locks in malloc implementations. And there is a lot of real-time code being written in C++.

jcelerier 8y ago

> fractionally less efficient std::function can potentially allocate memory and hides stuff behind a vtable, e.g. two indirections. That's not what I would call "frationally less efficient".

htfy96 8y ago
Personally I doubted about the overhead on nowadays machines. I guess a Electron app with a button definitely goes over more abstraction than several indirection when it is clicked. Should we really care about these overhead, at least on desktop platform?
quietbritishjim 8y ago
Perhaps "fractional" is the wrong word because has a literal meaning which probably isn't true if you compare calling a std::function vs calling a function directly within a template (although you still need to call that template from somewhere so you'll probably end up with at least one indirection, but I digress). But as a fraction of your application's overall runtime, in almost cases it's going to be an absolutely insignificant fraction, like less than a millionth of the runtime. This is certainly true if you're writing a GUI or a network-based server process. For it to be noticeable you'd have to be calling the callback in an extraordinarily tight loop, where the actual function does very little (less than a few pointer indirections!). Put another way, avoiding std::function is a classic case of premature optimisation.
- jcelerier 8y ago
  > This is certainly true if you're writing a GUI or a network-based server process. But are you writing those in C++ ? C++ is used exactly where you have those tight loops. Execution engines, VMs and interpreters... Besides, as soon as you want to have some real-time behaviour you can't have any call to malloc since it may make performance much less deterministic due to locks in malloc implementations. And there is a lot of real-time code being written in C++.