Compiling the code

  // start tmp.cpp
  template<class T,class S> struct A{};

  struct B
  {   
      void f(A<int,int> default_value=A<int,int>());
  };
  // end tmp.cpp

with

  g++ tmp.cpp

produces these errors

tmp.cpp:6: error: expected ‘,’ or ‘...’ before ‘>’ token
tmp.cpp:6: error: missing ‘>’ to terminate the template argument list
tmp.cpp:6: error: wrong number of template arguments (1, should be 2)
tmp.cpp:2: error: provided for ‘template<class T, class S> struct A’
tmp.cpp:6: error: expected ‘,’ before ‘int’

The errors disappear if
  1. The function is moved outside of the second struct definition.
  2. The second template argument to A is removed.
  3. The default argument is removed.
  4. A typedef is used to encapsulate A<int,int>.
  5. Comeau 4.3.3 is used.