[xyzzyz]

What kind of speed increase are you talking about? Your comment's logic seems to suggest that, for instance, C (a language without templates) is inherently slower than C++, which is not the case. Can you back your statements up with evidence?

[sreque]

Speed increases like those explained in http://www.tilander.org/aurora/2007/12/comparing-stdsort-and..., which compares qsort to std::sort.

Because templates are basically automated code copy-paste, the compiler can more easily inline at compile-time. Unfortunately, it also translates to lots more compiled code, which means slower compile times and fatter binaries. Still, writing something like the STL library in C with the same performance characteristics would be much more difficult, if not impossible.

I'm not a C++ expert, but that's my understanding of things, at least.

[pborges]

If you are worried about the performance hit caused by function calling through a function pointer you might want to give a look at http://sglib.sourceforge.net/.

[shin_lao]

Templates are much more powerful than C with macros.

Templates are more than copy/paste code, the compiler can make strong assumptions about the code path during the optimization phase because it's actual code.

It's not just a question of inlining calls but mainly a question of being able to remove branches altogether. Branches is the performance killer, remember?

Examples:

- with template specialization you can make "compile time" switches (horrible to reproduce with C + macros) - you can compute values at compile time (not quite possible in C + macros) - inlining permits copy elision (an optimization that doesn't exist in C since return by value is a non sequitur) - the CRTP is faster than an object with vtables because it avoids indirect calls - removing of dead branches, by inspecting the templates recursion, the compiler can determine which branches will never be taken and doesn't compile them - probably more!

[liuliu]

I think that he is talking about the cases where you can use template to avoid function pointer in C.