Memoizing a function with two inputs in C++

Question

I have a function, f(a,b), that accepts two inputs. I do not know ahead of time which values of a and b will be used. I'm okay with being a little wasteful on memory (I care about speed). I want to be able to check if the output of f(a,b) has already been delivered, and if so, deliver that output again without re-running through the f(a,b) process.

Trivially easy to do in Python with decorators, but C++ is way over my head here.

Answer 1

I would use a std::map (or maybe an std::unordered_map) whose key is a std::pair, or perhaps use a map of maps.

C++11 improvements are probably helpful in that case. Or maybe some Boost thing.