Callbacks in C++ using template functors (1994)

For a more modern form of this, take a look at Boost.Signals2. https://www.boost.org/doc/libs/1_68_0/doc/html/signals2.html It provides a slightly nicer interface in that signals can be defined in a single template argument, vs. splitting args / return type as separate template arguments. For example: boost::signals2::signal<void (float, float)> sig; would allow the following function as a slots: void do_something(float x, float y) { ... } There's also Qt's signal/slots implementation…

I know everyone here knows Rich Hickey from Clojure, but I'm a C/C++ programmer from the '90s and I primarily know him for "Hickey functors", which were the de facto standard way of doing object-oriented callbacks in C++. Also, while I am sure they were for the time a near-optimal solution, they are f'ing gross, so "Hickey functor" is a bit of an epithet. "Oh well, better than Hickey functors" was a justification for a lot of Gang-of-four pattern goop…

Heard about this watching Casey Muratori's "The Big OOPs" talk [0]. Thought it couldn't be _that_ Hickey, but turns out it was! [0] https://youtu.be/wo84LFzx5nI?si=SBv1UqgtKJ1BH3Cw&t=5159

Classic from Rich Hickey. I remember mugging this up for a C++ interview in late 96. It was state of the art then.