How to pass reference-to-function into another function

Question

Using function pointers as arguments for other functions has been discussed in the literature I've been reading.

How would you transmit a function by reference without using pointers, is the question I have.

I've been searching the Internet for the solution, but I haven't come up with a solid response.

I am aware that variables may be sent by reference using the syntax void funct(int& anInt);.

How would you proceed if the parameter was a reference to a function rather than a reference to a variable?

Additionally, how would you utilise a function body reference?