Returning from functions

In the previous sections we have seen how functions return values without going into detail. In this section we will take a closer look at how we can return data from a function.

There are two ways to return:

• Explicit Return
• Implicit Return

When returning data from a function the return types must match up with the return types declared in the function signature. This means that if the first return type is a u64 then the type of the first value being returned must also be a u64.

Explicit Return

To return from a function explicitly we use the return keyword followed by the arguments and a semi-colon.

fn main() -> bool {
    return true;
}

A return expression is typically used at the end of a function; however, it can be used earlier as a mechanism to exit a function early if some condition is met.

fn return_data(parameter_one: u64, parameter_two: bool) -> (bool, u64) {
    if parameter_two {
        return (!parameter_two, parameter_one + 42);
    }
    return (parameter_two, 42);
}

Implicit Return

To return from a function implicitly we do not use the return keyword and we omit the semi-colon at the end of the line.

fn main() -> bool {
    true
}

An implicit return is a special case of the explicit return. It can only be used at the end of a function.

fn return_data(parameter_one: u64, parameter_two: bool) -> (bool, u64) {
    if parameter_two {
        (!parameter_two, parameter_one + 42)
    } else {
        (parameter_two, 42)
    }
}