Will I be able to declare a constexpr lambda inside a template parameter?

Question

I know it\'s like opening the Pandora box but it doesn\'t stop bothering me. Consider a simple example:

#include 

template 
s         


        

Answer 1

In C++17 you can pass pointer to lambda function as template parameter with function pointer type:

# include 

template
int get_twice()
{
    return fn() * 2;
}

int main()
{
    int result = get_twice <+[]() { return 42; }> ();
    assert(result == 84);
}