I have always thought that auto in C++11 is a placeholder for the actual data type, but it appears not so in the following:

tuple<int, int> permute(int a, int b){return {b,a};}
int main(){
   auto [x,y] = permute(2,5);
   cout<<x<<","<<y<<endl;
   tuple<int, int> {x,y} = permute(2,5);
   cout<<x<<","<<y<<endl;
   return 0;
   }

Why auto requires [ , ] while a tuple requires curly brackets?