Since php version 8.4.0 we can declare properties inside a interface but the properties must specified as readable, writeable or both

interface I
{
    // An implementing class MUST have a publicly-readable property,
    // but whether or not it's publicly settable is unrestricted.
    public string $readable { get; }

    // An implementing class MUST have a publicly-writeable property,
    // but whether or not it's publicly readable is unrestricted.
    public string $writeable { set; }

    // An implementing class MUST have a property that is both publicly
    // readable and publicly writeable.
    public string $both { get; set; }
}

// This class implements all three properties as traditional, un-hooked
// properties. That's entirely valid.
class C1 implements I
{
    public string $readable;

    public string $writeable;

    public string $both;
}