Hacker News Reader

I'd like to introduce you to the wonderful world of templates.

But that's the thing, you have complete control over templates, there's no compiler magic involved. If you're unhappy with the way a template call sequence gets optimized you can tweak it completely. In your comment below you mention boost but that's kind of my point: boost is a completely optional third party library, not a built-in construct of the language like the coroutines discussed here. Boost might be relying on the compiler correctly optimizing some constructs but the C++ template mechanics themselves not so much.

Do you have any examples of templates incurring a runtime cost at -O0 compared to a “no templates” approach?

Expression templates (ala boost::spirit) definitely come to mind. The callstack in a -O0 build can get very, very deep.

Heck just using std::numeric_limits<int>::min() will incur a function call in -O0, but nobody cares since it gets optimized in -O1 and up. The same thing applies more and more as you invoke templates from templates, but, again, nobody cares since we are confident it'll get optimized/inlined easily.

It's not nearly as prevalent in modern code since constexpr static variables are now a thing, but relying on these optimizations has historically been super important.

Reply on news.ycombinator.com