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Date: Sat, 6 Apr 2024 14:43:43 +0100
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Subject: Re: [PHP-DEV] [RFC] [Discussion] Support object type in BCMath
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From: imsop.php@rwec.co.uk ("Rowan Tommins [IMSoP]")

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On 06/04/2024 07:24, Saki Takamachi wrote:
> Take a look at the methods shown below:
> ```
> protected static function resultPropertyRules(string $propertyName,
> mixed $value1, mixed $value2): mixed {}
> ```
>
> This method determines which operand value to use in the result after
> calculation for a property that the user has defined by extending the
> class.


While this is an intriguing idea, it only solves a narrow set of use 
cases. For instance:

- The class might want different behaviour for different operations; 
e.g. Money(42, 'USD') + Money(42, 'USD') should give Money(84, 'USD'); 
but Money(42, 'USD') * Money(42, 'USD') should be an error.

- Properties might need to interact with each other; e.g. Distance(2, 
'metres') + Distance(2, 'feet') could result in Distance(2.6096, 
'metres'); but if you calculate one property at a time, you'll end up 
with Distance(4, 'metres'), which is clearly wrong.

The fundamental problem is that it ignores the OOP concept of 
encapsulation: how an object stores its internal state should not define 
its behaviour. Instead, the object should be able to directly define 
behaviour for the operations it supports.

Regards,

-- 
Rowan Tommins
[IMSoP]

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    <div class="moz-cite-prefix">On 06/04/2024 07:24, Saki Takamachi
      wrote:<br>
    </div>
    <blockquote type="cite"
      cite="mid:FF0FFBCE-7F03-44A2-B7AE-D3F958135ACB@sakiot.com">
      <pre>Take a look at the methods shown below:
```
protected static function resultPropertyRules(string $propertyName, 
mixed $value1, mixed $value2): mixed {}
```

This method determines which operand value to use in the result after 
calculation for a property that the user has defined by extending the 
class.</pre>
    </blockquote>
    <p><br>
    </p>
    <p>While this is an intriguing idea, it only solves a narrow set of
      use cases. For instance:<br>
    </p>
    <p>- The class might want different behaviour for different
      operations; e.g. Money(42, 'USD') + Money(42, 'USD') should give
      Money(84, 'USD'); but Money(42, 'USD') * Money(42, 'USD') should
      be an error.</p>
    <p>- Properties might need to interact with each other; e.g.
      Distance(2, 'metres') + Distance(2, 'feet') could result in
      Distance(2.6096, 'metres'); but if you calculate one property at a
      time, you'll end up with Distance(4, 'metres'), which is clearly
      wrong.</p>
    <p>The fundamental problem is that it ignores the OOP concept of
      encapsulation: how an object stores its internal state should not
      define its behaviour. Instead, the object should be able to
      directly define behaviour for the operations it supports.<br>
    </p>
    <p>Regards,<br>
    </p>
    <pre class="moz-signature" cols="72">-- 
Rowan Tommins
[IMSoP]</pre>
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