Early Return? Let's dive deep!

Zabir Anik — Sat, 19 Mar 2022 03:34:48 +0000

The problem

Let's think of a system, where a user should be able to create a new account if the following validations are passed:

the username is valid
the email is valid
the phone is valid and verified

Here's an example of a scenario while constructing the create_account function, the primary thought process was to validate the corresponding requirements until arrived at the desired outcome.

function create_account( $user_name, $email, $phone_number ) {
    if ( $user_name->is_valid() ) {
        if ( $email->is_valid() ) {
            if ( $phone_number->is_valid() ) {
                $is_verified = send_verification_code( $phone_number );

                if ( $is_verified ) {
                    // Finally, create the account.
                } else {
                    // Handle verification error.
                }
            } else {
                // Handle invalid phone.
            }
        } else {
            // Handle invalid email.
        }
    } else {
        // Handle invalid user name.
    }
}

All right, we served the requirements and constructed a function which does exactly what we needed. But What can be observed in this approach?

It's tough to figure out which "else" goes with each "if," making error handling difficult to read, especially when the "if" block is long
Arrow anti-pattern: because of nested conditions and loops, the code begins to resemble an arrow

The Solution

Let's rethink and take a different perspective to refactor the code.

Return early is the way of writing functions or methods so that the expected positive result is returned at the end of the function and the rest of the code terminates the execution (by returning or throwing an exception) when conditions are not met

function create_account( $user_name, $email, $phone_number ) {
    if ( ! $user_name->is_valid() ) {
        // Handle invalid user name.
        return;
    }

    if ( ! $email->is_valid() ) {
        // Handle invalid email.
        return;
    }

    if ( ! $phone_number->is_valid() ) {
        // Handle invalid phone.
        return;
    }

    $is_verified = send_verification_code( $phone_number );

    if ( ! $is_verified ) {
        // Handle verification error.
             return;
    }

    // Finally, create the account.
}

This is performed by:

Reversing the "if" conditions
Handling the relevant errors
Returning or throwing an appropriate exception, thus completing the function's execution

Let's analysis the new approach:

There is only one level of indentation in the code. It is feasible to read it in a straight line.
The expected positive outcome is easily found at the function's conclusion
This approach places a greater emphasis on locating mistakes first and then carefully implementing business logic subsequently, resulting in fewer bugs
On errors, the function terminates quickly, preventing the execution of more code unintentionally

Conclusion

The "return early" pattern is a great approach to avoid functions becoming too complicated. This does not, however, imply that it can be used at all times. Even with the option of isolating the code to other functions, it is unavoidable to have certain nested "ifs" throughout sophisticated business logic.