Is there a way to enforce the type of an object returned by a function that could return anything?

In addition to what Tom already said, using instanceof has worked quite well for me. (Actually never heard of is_a() before.)

if (is_singular() && $queried_object instanceof \WP_Post) {
    // do something
}

Both PHPStan and my IDE know that after this check, $queried_object is an instance of the WP_Post class.

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