Do you have any evidence of this? I've read somewhere that Visual 8 does something like this, but I hope this is not the COMDAT folding option. This redundant machine code erasing is performed by the linker, the code is still instantiated at compile time, so we are not going to save much compilation time.
No, it's not some new esoteric thing: Given some code like
template<typename T> struct X { /* code inside that only uses T* */ }
the compiler can determine that an incomplete type suffices for 'T' and that instances for any 'T' are interchangeable.
I tried with std::vector<type*> (cf joined source file) and it is the COMDAT folding which do the work: Without: 36ko With: 28ko (the others options by default, in particular Win98 optimization is on bumping the size) The COMDAT folding is on by default. I don't know how much this affect the compile time, but at least it should greatly reduce the code bloat. It could break some code: template< class T > void testFct(T t) { std::cout << t << std::endl; } ... std::cout << "ptr1: " << static_cast< void(*)(t1*)
(&testFct<t1*>) << std::endl; std::cout << "ptr2: " << static_cast< void(*)(t2*) (&testFct<t2*>) << std::endl;
with COMDAT folding the function address are the same (not without) (using VS8) Regards, -- Cédric Venet