Class constants allow narrowing override from untyped to typed

[khaledalam]

Description

Ref: RFC: typed_class_constants

The following code https://3v4l.org/MUm1l:

<?php

// overriding an untyped parent constant with a typed one

class A {
    public const VALUE = 42; // untyped
}

class B extends A {
    public const float VALUE = 42.5; // narrowing to `float`
}

echo "Parent type: " . gettype(A::VALUE) . "\n";
echo "Child value: " . B::VALUE . "\n";

Resulted in this output:

Parent type: integer
Child value: 42.5

But I expected this output instead:

Fatal error: Cannot override constant A::VALUE with incompatible type in %s on line %d

PHP Version

8.3.0 - 8.3.23, 8.4.1 - 8.4.10

Operating System

No response

[khaledalam]

Also https://3v4l.org/nDD3o:

<?php

class A {
    private const int VALUE = 42;
}

class B extends A {
    public const string VALUE = 'override';
}

echo B::VALUE;

output: override

[khaledalam]

https://3v4l.org/8ksmu

<?php


class A {
    protected const int VALUE = 42;
}

class B extends A {
    public const string VALUE = 'oops';
}

output: Fatal error: Type of B::VALUE must be compatible with A::VALUE of type int in /in/8ksmu on line 8

[iluuu1994]

Hi @khaledalam. Class contants are covariant. Narrowing is allowed for the same reason narrowing is allowed for return types: The value is only read but never set. A private parent class constant is not overridden, it's shadowed.

[khaledalam]

@iluuu1994 Thanks for the clarification