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

I suggest using Boost's static assert feature in concert with is_base_of from the Boost Type Traits library:

template
class ObservableList {
    BOOST_STATIC_ASSERT((is_base_of::value)); //Yes, the double parentheses are needed, otherwise the comma will be seen as macro argument separator
    ...
};

In some other, simpler cases, you can simply forward-declare a global template, but only define (explicitly or partially specialise) it for the valid types:

template class my_template;     // Declare, but don't define

// int is a valid type
template<> class my_template {
    ...
};

// All pointer types are valid
template class my_template {
    ...
};

// All other types are invalid, and will cause linker error messages.

[Minor EDIT 6/12/2013: Using a declared-but-not-defined template will result in linker, not compiler, error messages.]