C++ Tips : Trailing Return Type

My C++ Tips

Trailing Return Type

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Trailing Return Type

• A way to specify the return type of a function after the parameter list.
• Useful when the return type depends on the types of the parameters

auto add(int a, int b) -> int 
{
    return a + b;
}

Why it’s important?

• When the return type depends on the parameter types.

template <typename T, typename U>
decltype(a * b) multiply(T a, U b) 
{   // ERROR: 'a' and 'b' not yet declared
    return a * b;
}

template <typename T, typename U>
auto multiply(T a, U b) -> decltype(a * b) 
{
    // OK. Because decltype(a * b) needs a and b to already exist in the scope, 
    // which only happens after the parameter list.
    return a * b;
}