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# Property accessor and mutator functions.
Property accessors and mutators are commonly referred to as "getter" and "setter" functions. This library uses [PHP's Magic Methods][magic-methods] to easily hook up getter and setter functions that are exposed externally as normal properties, via the `MagicProp` trait.
Why? This kind of functionality can certainly be seen as a hack, but sometimes hacks are necessary. Specifically PHP.Gt is implementing [the DOM standard in PHP][dom] which requires certain properties to have "live" or "readonly" functionality, which is only possible using magic __get and __set functions. This library simply holds the reusable behaviour for other repositories that require it.
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Example usage: Read-only properties that are calculated upon access
-------------------------------------------------------------------
See the class `Day` below, which represents a day in time:
```php
use Gt\PropFunc\MagicProp;
/**
* @property-read bool $future True if the day is in the future
* @property-read int $daysApart Days between now and this day
*/
class Day {
use MagicProp;
public function __construct(
private DateTimeInterface $dateTime
) {}
// Expose the "dateTime" private property with read-only access:
private function __prop_get_dateTime():DateTimeInterface {
return $this->dateTime;
}
// Expose the "future" calculated property with read-only access:
private function __prop_get_future():bool {
$now = new DateTime();
return $now < $this->dateTime;
}
// Expose the "daysApart" calculated property with read-only access:
private function __prop_get_daysApart():int {
$now = new DateTime();
$diff = $now->diff($this->dateTime);
return $diff->days;
}
}
```
See the code below which uses the `Day` class. It can access the properties, but not mutate them.
```php
$day = new Day($dateTime);
echo "Day is $day->diff days in the ";
echo $day->future ? "future" : "past";
echo PHP_EOL;
$day->diff = 10;
echo "Exception thrown on line above!";
```
Usages
------
+ Read only properties - as with the above example, properties can be made read-only. This feature is [coming to the PHP language][write-once-property-rfc], but without the ability to define the accessor logic.
+ Live properties - if a property's value is required to update depending on certain conditions, a getter function is required.
+ Property validation - if a property's value can't simply be validated by its type alone, the setter function can be used to ensure the value meets validation criteria.
[magic-methods]: https://www.php.net/manual/en/language.oop5.magic.php
[dom]: https://www.php.gt/dom
[write-once-property-rfc]: https://wiki.php.net/rfc/write_once_properties