[WIP] Prototype: Support object types in BCMath

[SakiTakamachi]

Please see https://externals.io/message/122651

(This is a branch derived from #13096.)

[zmitic]

Sorry for barging as end-user, but I am really interested if this RFC will allow lazy evaluation.

For example:

class LazyInt extends Number
{
	private int|null $cachedValue = null;

    /** 
     * @param Closure(): int $closure 
     */
    public function __construct(private Closure $closure){}

	#[Override]
    public function getValue(): int
    {
        return $this->cachedValue ??= ($this->closure)(); // one-time lazy evaluation
    }
}

and then use like:

function slow(): int
{
	sleep(5); // some slow query

	return 42;
}

$lazy1 = new LazyInt(fn() => slow()); // nothing happens
$lazy2 = new LazyInt(fn() => slow()); // nothing happens

$lazy1 + $lazy2; // sleeps 10 seconds, returns Number(84);
$lazy1 + $lazy2; // no sleep, returns Number(84);

---

This lazy evaluation has many use-cases, but it would require something like this:

class Number extends \Stringable
{
	public function getValue(): string|int;
}

[SakiTakamachi]

@zmitic

After much discussion, it was decided that this class should be marked final, so it cannot be inherited :)

https://wiki.php.net/rfc/support_object_type_in_bcmath

[zmitic]

@SakiTakamachi
Thanks, I thought it was still under discussion but externals are too hard to read with nested comments.

Last one, I promise: will you be open to create NumberInterface that users could implement? This would open the door to many new things. But by locking users from custom implementations, I think that operator overload will never become a thing.