PHP return type hinting, object OR a boolean? [duplicate]

Question

So I know that I can do return type hinting in php7. I can do an object return hint with:

function getUser($pdo, $username) : User
{

}

where User is the object being returned.

However, if the user isn't found in the SQL, returning 'false' instead of a User object gives:

Uncaught TypeError: Return value of UserFind::findUser() must be an instance of User, boolean returned

But what if the SQL can't find the user? How can I return a boolean, false, if the user doesn't exist? Should I just ignore return type hinting in this scenario?

EDIT: I looked at the other question, 'Nullable return types in php 7' and while my question is almost identical, I want to extend my question by asking if there would ever be a way to return one of two types. For example return an object or a string if the object is nonexistant?

Answer 1

What you're talking about is called a Union Type. There's considerable discussion about it in Internals

This RFC proposes the ability to define multiple possible types for a parameter or return type and calls them “union types”. A value passes the type-check for a union type if the value would pass any one of the members the union. A vertical bar (OR) is placed between each of the two or more types.

Here is an example of a parameter accepting either an array or a Traversable and no other types:

function (Array | Traversable $in) {
    foreach ($in as $value) {
        echo $value, PHP_EOL;
    }
}

There can be more than two types in the union. As an example, it is somewhat common for a routine that interacts with a database to have one of three results:

1. Successfully found results
2. Successfully found no results
3. There was an error

This is all targeted at PHP 7.1 but isn't up for a vote yet (let alone looking like it will pass).

So what about your issue? I would say, at least for now, don't type hint your return. Just issue a doc block that says it can return User or false

/**
 * @param \PDO $pdo
 * @param string $username
 * @return User|false
 */