Re: simple ?

Avec CLang c'est un peu plus explicite :

main.cpp:4:20: error: 'auto' not allowed in lambda parameter
 auto square = [](auto x) { return x * x; };
 ^~~~
main.cpp:5:19: error: 'auto' not allowed in lambda parameter
 auto twice = [](auto x, auto f) { return f(x) + f(x); };
 ^~~~
main.cpp:5:27: error: 'auto' not allowed in lambda parameter
 auto twice = [](auto x, auto f) { return f(x) + f(x); };
 ^~~~
main.cpp:7:16: error: no matching function for call to object of type '<lambda at main.cpp:5:16>'
 std::cout << twice(5,square) << std::endl;
 ^~~~~
main.cpp:5:16: note: candidate template ignored: couldn't infer template argument '$auto-0-0'
 auto twice = [](auto x, auto f) { return f(x) + f(x); };
 ^
main.cpp:8:16: error: no matching function for call to object of type '<lambda at main.cpp:5:16>'
 std::cout << twice(5.1,square) << std::endl;
 ^~~~~
main.cpp:5:16: note: candidate template ignored: couldn't infer template argument '$auto-0-0'
 auto twice = [](auto x, auto f) { return f(x) + f(x); };