Never

never is a return-only type indicating the function does not terminate. This means that it either calls exit, throws an exception, or is an infinite loop. Therefore, it cannot be part of a union type declaration. Available as of PHP 8.1.0.

A return statement in a never function is a compile-time error, even if the return would not be reached during execution. If control flow reaches the end of a never function without exiting, throwing an exception, or entering an infinite loop, a TypeError is thrown.

never is, in type theory parlance, the bottom type, meaning it is the subtype of every other type and can replace any other return type during inheritance.