What do compilers do with compile-time branching?

Question

EDIT: I took the \"if/else\" case as an example that can sometimes be resolved at compile time (eg when static values are involved, cf

Answer 1

Credit to @MooingDuck and @Casey

template
decltype(auto) if_else_impl(std::true_type, FN1 &&fn1, FN2 &&, Args&&... args)
{
    return fn1(std::forward(args)...);
}

template
decltype(auto) if_else_impl(std::false_type, FN1 &&, FN2 &&fn2, Args&&... args)
{
    return fn2(std::forward(args)...);
}

#define static_if(...) if_else_impl(__VA_ARGS__, *this)

And ussage as simple as:

static_if(do_it,
    [&](auto& self){ return 1; },
    [&](auto& self){ return self.sum(2); }
);

Works as static if - compiler go only to "true" branch.

---

P.S. You need to have self = *this and make member calls from it, due to gcc bug . If you'll have nested lambda calls you can't use this-> instead of self.