dawn dust
I'm looking at the following piece of code written by a colleague.
template <size_t N> struct Apply {
template <typename F, typename T> static FORCE_INLINE void apply(F &&f, T &&t) {
Apply<N - 1>::apply(::std::forward<F>(f), ::std::forward<T>(t));
::std::forward<F>(f)(::std::get<N>(::std::forward<T>(t)));
}
};
Am I correct in thinking that there is a use after move of f here?
dawn dust
This code was being used for essentially, applying a functor f(x) for each entry in a tuple. I've not used std::apply before, but I thought this would do the job to replace it
template <typename Function, typename Tuple>
constexpr void apply(Function &&f, Tuple &&t) {
std::apply([&f](auto &&...x) { (f(x), ...); }, std::forward<Tuple>(t));
}
Any gotcha I need to be aware of here?
viral lake
I mean, lgtm. just not sure why this would exist. looks like you might as well just use std::apply instead of this?
the only difference i see between this and std::apply is that this one returns void
dawn dust
I mean, lgtm. just not sure why this would exist. looks like you might as well j...
It's just so that the callee doesn't have to type out the lambda everytime this is needed.
dawn dust
yep
upbeat dome
you can't really forward the same thing twice
why not?
viral lake
because the first forward might result in a move, then what?
upbeat dome
hmmmmm
viral lake
forwarding the same thing more than once is pretty much never not a bug
viral lake
yeah, i also often didn't ^^
upbeat dome
when are forward references useful then?
viral lake
when you want to perfectly just forward a thing
upbeat dome
why would i need to do that
viral lake
forward meaning immediately hand it off to the next guy
viral lake
why would i need to do that
because you're just passing it on to some other function that might differentiate based on whether the original thing was an lvalue or rvalue.
the purpose of std::forward is to forward a thing in a way that preserves the value category of the original thing.
upbeat dome
because you're just passing it on to some other function that might differentiat...
hmmmmmm so it seems, then, to be far less often used than i thought?
upbeat dome
i see
feral prawn