What is an example of a Value Object in PHP?
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26-05-2021 - |
質問
I have read plenty of C# examples of Value Objects, and I understand that it is an "object" that is identified by it's values. If a value changes, the object is "new".
However, that doesn't seem to make sense when it comes to PHP...either that, or I'm just not making the connection.
Is a Value Object just a string?
解決
To put this into context, in many OO languages, objects are compared by their identity. In pseudocode:
bar = new Foo
baz = new Foo
bar == baz // false
Even though both objects are basically the same if you just look at their values, they're not considered to be identical, because they are separate instances. To demonstrate:
bar = new Foo
baz = bar
bar == baz // true
Now:
In computer science, a value object is a small simple object, like money or a date range, whose equality isn't based on identity.
This would be a demonstration of "value objects":
address1 = new Address('Main street 42')
address2 = new Address('Main street 42')
address1 == address2 // true
Because the values are the same, both objects are considered equal, even if they're separate instances.
PHP does not have a separate concept of "value objects", it only has one type of object. Its comparison operator can make that distinction though:
When using the comparison operator (==), object variables are compared in a simple manner, namely: Two object instances are equal if they have the same attributes and values, and are instances of the same class.
http://www.php.net/manual/en/language.oop5.object-comparison.php
E.g.:
$address1 = new Address('Main street 42');
$address2 = new Address('Main street 42');
$address1 == $address2; // true equal...
$address1 === $address2; // false ...but not identical
他のヒント
PHP used to have value objects but that was back in PHP4. See http://3v4l.org/ghI8G