decltype is used to get the type of a expression
Considering the following function
typedef<typename T1, typename T2>
T1 add(T1 a, T2 b) {
return a + b;
}
For the following 2 invocations
add(1, 1.5); add(1.5, 1);
The results will be different,
2 2.5
To solve this problem, we can use decltype, the return type should be type of the expression a + b.
typedef<typename T1, typename T2>
auto add(T1 a, T2 b) -> decltype(a + b) {
return a + b;
}