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Date: Fri, 5 Apr 2024 11:57:53 +0100
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Subject: Re: [PHP-DEV] [RFC] [Discussion] Support object type in BCMath
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From: barney@redmagic.org.uk (Barney Laurance)


On 05/04/2024 10:48, Tim Düsterhus wrote:
>
> Your `Money` example would allow for unsound and/or non-sense 
> behavior, such as:
>
>     $fiveEuros = new Money(5, 'EUR');
>     $tenDollars = new Money(10, 'EUR');
>
>     $what = $fiveEuros + $tenDollars;
>
> What would you expect to be in $what? A `BcMath\Number(15)`?
>

Yep, since the add method is final and will return a Number then 
Number(15) is the only possible result. And even if you did `(new 
Money(5, 'EUR')) + (new Money(15, 'EUR'))`, the result would be the 
Number 15, not a money. Equally if it was extended to add the isPrime 
method as soon as you do any calculation on it you'd get a number 
without the isPrime method, so it would be of very limited use. That 
could be avoided by returning `static` instead of `self`, but that's 
makes addition non-commutative which would be confusing, and using `new 
static` sort of requires the constructor to be final, which would make 
the Money case impossible.

So yes I'd say you've convinced me that the Number class does need to be 
a Final class.