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PHP 7.4 Typed Properties BC Problems

Updated: April 25, 2024 20:52

Published: December 27, 2019 02:13

If you’re not aware, PHP 7.4 has introduced Typed Properties. But buyer beware, there‘s a hitch...

Prior to PHP 7.4, declaring property scalar types was done with DocBlocks as follows:

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/** @var int|null **/
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public $id;
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With typed properties introduced in PHP 7.4, the scalar type can now be set like this:

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public ?int $id;
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This is awesome, it cuts down on excessive boilerplate and the PHP interpreter will not allow an invalid value to be set on the property.

But, there are a couple caveats to be aware of...

Without setting a property type, one would be able to have a class property such as:

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// MyClass.php
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<?php
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class MyClass {
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/** @var int|null **/
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public $id;
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}
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And then call the property without any problems like:

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// test.php
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<?php
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require('MyClass.php');
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$object = new MyClass;
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$var = $object->id;
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var_dump($var);
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$:> php -f test.php
NULL

However, if you declare the property type and then attempt to access that type as above, you'll get a FatalError. I.e.

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// test.php
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<?php
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class MyClass {
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public ?int $id;
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}
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$object = new MyClass;
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$var = $object->int;
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echo $var;
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$:> php -f test.php
Fatal error: Uncaught Error: Typed property MyClass::$id must not be accessed before initialization...

To overcome this, you must set the value of $id before attempting to access it. This can be accomplished in a number of ways.

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class MyClass
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{
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public ?int $id = null;
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}
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class MyClass
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{
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public ?int $id;
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public function __construct() {
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$this->id = null;
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}
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}
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class MyClass {
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public ?int $id;
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public function setId(?int $id) {
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$this->id = $id;
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}
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}
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Using any of the above means of setting $id before accessing the value of $id would result in the following:

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// MyClass.php
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<?php
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class MyClass {
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public ?int $id = null;
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}
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$object = new MyClass;
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$var = $object->id;
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var_dump($var;)
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$:> php -f  MyClass.php
NULL

Of course if you are using setter's to set the value of $id , you must call the setter method before accessing the property.

- Jesse Rushlow [email protected]