what are the differences between returning auto, auto&, auto&& and decltype(auto)?

[JUANDENT]

what are the differences between returning auto, auto&, auto&& and decltype(auto)?

for instance:

auto f(int val) { 
static int value = val;
return value;
}
auto& f(int val) { 
static int value = val;
return value;
}
auto&& f(int val) { 
static int value = val;
return value;
}
decltype(auto) f(int val) { 
static int value = val;
return value;
}

??

[deleted account xyzzy]

For auto and decltype(auto):

https://stackoverflow.com/questions/21369113/what-is-the-difference-between-auto-and-decltypeauto-when-returning-from-a-fun

Also: https://cplusplus.com/forum/general/188645/

auto, auto& and auto&&:

https://stackoverflow.com/questions/29859796/c-auto-vs-auto