How can I make a class method that takes a function as a parameter? [duplicate]

Question

I want to create a method inside a class (but I think this is irrelevant) that sorts a vector according to the bool value returned by a particular function... I read that it is possible but I don't know how to do it...

I would like to call the function and put (for example) >, or <, as a parameter, so that I don't have to create two almost identical functions.

How I imagine the body of the function:

for (int i = 0 ; i < DIM - j; i++) { if (some_function(v[i], v[i+1])) { int temp; temp = v[i]; v[i] = v[i+1]; v[i+1] = temp; } }

@AdrianMole: There are other techniques for C++. E.g. functors, std::function, lambdas. — Bathsheba
– Bathsheba, Commented Jul 10, 2020 at 14:34
The C dupe is a poor choice, especially if this is an X/Y question (i.e. reinventing the wheel). — underscore_d
– underscore_d, Commented Jul 10, 2020 at 14:36
@underscore_d I looked for a C++ dupe, but that just pointed to the C version: stackoverflow.com/q/6339970/10871073 — Adrian Mole
– Adrian Mole, Commented Jul 10, 2020 at 14:37

cigien · Accepted Answer · 2020-07-10 14:33:35Z

You can do this by passing in a function object:

template <typename Op> void f(Op op) { // ... if (op(v[i], v[i+1])) // ... }

and call it like this:

f(std::less{}); // for < f(std::greater{}); // for >

Of course, f here is just an example, but you just need to add a template parameter to your own function in this way.

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