I was watching this video on a topic about C++17's Variadic using. So out of curiosity I tried this code snippet here exactly as is within my own IDE MS Visual Studio 2017 CE with compiler language settings to c++17.
#include <iostream>
#include <utility>
template<typename ... B>
struct Merged : B... {
template<typename ... T>
Merged( T && ... t ) : B( std::forward<T>( t ) )... {
}
using B::operator()...;
};
template<typename ... T>
Merged( T... ) -> Merged<std::decay_t<T>...>;
int main() {
const auto l1 = []() { return 4; };
const auto l2 = []( const int i ) { return i * 10; };
Merged merged( l1, l2, []( const double d ) { return d * 3.2; } );
std::cout << merged() << "\n";
std::cout << merged( 5 ) << "\n";
std::cout << merged( 4.5 ) << "\n";
return 0;
}
Of course it fails to compile. So I then ventured to websites with built in compilers. I tried using Compiler Explorer and I used a majority of the compiler versions available on that website setting the appropriate compiler options for c++17. They all failed to compile. I eventually tried WandBox
and it only seems to compile for Clang versions 5.0 and higher. None of the GCC compilers would compile it from either Compiler Explorer or WandBox, and the only compilers that would compile and run it as is are the Clang compilers at WandBox.
I'm not interested in actually trying to make this work; I was just curious or interested in the subject of the video itself. When I tried to implement the code it became vary curious and apparent on how much of a variation there is from one compiler of the C++ language to another.
Why does it appear in this specific case that Clang's versions 5.0+ are the only ones to fully support this feature of the C++17 language with the syntax currently being the way it is?
