Question

Possible Duplicate:
Trouble with template parameters used in macros

I’m trying to figure out a way to get this to work without changing the structure of INHERIT:

#define INHERIT(t) foo<t>
template<typename A, typename B>
struct bar : INHERIT(bar<A, B>) {};

The problem is that the invocation of INHERIT contains a comma.

I’m trying to support older compilers so variadic macros and template aliases are not an option. Is there anyway to fix this?

Answer 1

Use a little tricky macros:

#define A2(t1,t2) t1,t2
#define A3(t1,t2,t3) t1,t2,t3
#define A4(t1,t2,t3,t4) t1,t2,t3,t4
#define INHERIT(t) foo< t >
template<typename A, typename B>
struct bar : INHERIT(bar<A2(A, B)>) {};

These macros cause that preprocessor stop treating comma as its syntax – the comma starts be treated as just part of argument.

An alternative way:

#define bar_A_B bar<A,B>
template<typename A, typename B>
struct bar : INHERIT(bar_A_B) {};

NOTE
These examples these does not compile without:

template <class T>
class foo {};