How to template'ize variable NAMES, not types?

Question

my question is about how to template'ize the name of a class member that should be used.

Maybe a simplified & pseudo example:

/** 
Does something with a specified member of every element in a List.
*/
template<membername MEMBER> // <-- How to define such thing?
void doSomething(std::vector<MyClass> all){

    for( i=0; i < all.size(); i++)
      all[i].MEMBER++; // e.g.; use all[i].MEMBER in same way

}

and

class MyClass{
public:
    int aaa, bbb, ccc;
}

and the application:

main(){
    vector<MyClass> all = ....

    // applicate doSomething() to all aaa's
    doSomething<aaa>(all);  // or:
    doSomething<MyClass::aaa>(all); // or:
    doSomething<?????>(all);
}

How should the template definition looks like, that I can switch which member variable (aaa, bbb or ccc) of MyClass is accessed/modified in doSomething(.) ?
In my real world task all MEMBER are of same type, as above.

Thanks, Tebas

Answer 1

Template parameters are restricted to types, integer constants, pointers/references to functions or objects with external linkage and member pointers -- but no identifiers.

But you could use a member pointer as template parameter:

template<int MyClass::* MemPtr>
void doSomething(std::vector<MyClass> & all) {
   for( i=0; i < all.size(); i++)
      (all[i].*MemPtr)++;
}

:

doSomething<&MyClass::aaa>(all);

Note that I changed the doSomething function to take a reference instead of accepting the vector by value.