Let's say I have this function:
constexpr void foo(size_t x)
{ }
And this template:
template<size_t X>
class bar;
Would it be possible to instantiate an instance of template bar with the constexpr size_t x inside the foo function if I know that I will always constexpr evaluate that function (C++17)?
If I understand you correctly you want this:
constexpr void foo(size_t x)
{
bar<x> b{};
}
This is not possible because a constexpr function can be evaluated at runtime, in which case the argument x is not a compile time constant.
What you need to do is make the argument a template argument instead:
template <size_t X>
constexpr void foo()
{
bar<x> b{};
}
// call it like this:
auto test()
{
foo<24>();
}
foo like this?x template argument all the way.