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Let's suppose I have a struct like this: struct my_struct { int a; int b; } I have a function which should set a new value for either "a" or "b". This function also requires to specify which variable to set. A typical example would be like this: void f(int which, my_struct* s, int new_value) { if(which == 0) s->a = new_value; else s->b = new_value; } For reasons I won't write here I cannot pass the pointer to a/b to f. So I cannot call f with address of my_struct::a or my_struct::b. Another thing I cannot do is to declare a vector (int vars[2]) within my_struct and pass an integer as index to f. Basically in f I need to access the variables by name. Problem with previous example is that in the future I plan to add more variables to struct and in that case I shall remember to add more if statements to f, which is bad for portability. A thing I could do is write f as a macro, like this: #define FUNC(which) void f(my_struct* s, int new_value) \ { \ s->which = new_value; \ } and then I could call FUNC(a) or FUNC(b). This would work but I don't like using macros. So my question is: Is there a way to achieve the same goal using templates instead of macros? EDIT : I'll try to explain why I cannot use pointers and I need access to variable by name. Basically the structure contains the state of a system. This systems needs to "undo" its state when requested. Undo is handled using an interface called undo_token like this: class undo_token { public: void undo(my_struct* s) = 0; }; So I cannot pass pointers to the undo method because of polymorphism (mystruct contains variables of other types as well). When I add a new variable to the structure I generally also add a new class, like this: class undo_a : public undo_token { int new_valu

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