//https://vittorioromeo.info/index/blog/passing_functions_to_functions.html
template <typename TSignature>
class function_view;
template <typename TReturn, typename... TArgs>
class function_view<TReturn(TArgs...)> final
{
private:
using signature_type = TReturn(void*, TArgs...);
void* _ptr;
TReturn (*_erased_fn)(void*, TArgs...);
public:
template <typename T, typename = std::enable_if_t<
std::is_callable<T&(TArgs...)>{} &&
!std::is_same<std::decay_t<T>, function_view>{}>>
function_view(T&& x) noexcept : _ptr{(void*)std::addressof(x)}
{
_erased_fn = [](void* ptr, TArgs... xs) -> TReturn {
return (*reinterpret_cast<std::add_pointer_t<T>>(ptr))(
std::forward<TArgs>(xs)...);
};
}
decltype(auto) operator()(TArgs... xs) const
noexcept(noexcept(_erased_fn(_ptr, std::forward<TArgs>(xs)...)))
{
return _erased_fn(_ptr, std::forward<TArgs>(xs)...);
}
};
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