C++ templates that accept only certain types

Question

In Java you can define generic class that accept only types that extends class of your choice, eg:

public class ObservableList {
  ...
         


        

Answer 1

C++20 concept usage

https://en.cppreference.com/w/cpp/language/constraints cppreference is giving the inheritance use case as an explicit concept example:

template 
concept Derived = std::is_base_of::value;
 
template T>
void f(T);  // T is constrained by Derived

For multiple bases I'm guessing the syntax will be:

template 
concept Derived = std::is_base_of::value || std::is_base_of::value;
 
template T>
void f(T);

GCC 10 appears to have implemented it: https://gcc.gnu.org/gcc-10/changes.html and you can get it as a PPA on Ubuntu 20.04. https://godbolt.org/ My local GCC 10.1 did not recognize concept yet, so not sure what is going on.