assign.propertyPrivateSet

Code example

<?php declare(strict_types = 1);

class Foo
{
	public private(set) int $value = 0;
}

function doFoo(Foo $foo): void
{
	$foo->value = 5;
}

Why is it reported?

The property uses asymmetric visibility with private(set), meaning it can be read publicly but can only be written to from within the declaring class itself. The code is attempting to assign a value to this property from outside the class, which violates the write visibility restriction.

Asymmetric visibility is a PHP 8.4+ feature that allows separate read and write access levels for properties.

In the example above, $foo->value is publicly readable but can only be assigned from within Foo. The assignment in doFoo() is outside the class and therefore not allowed.

How to fix it

Use a public method on the class to modify the property:

 <?php declare(strict_types = 1);

 class Foo
 {
 	public private(set) int $value = 0;

+	public function setValue(int $value): void
+	{
+		$this->value = $value;
+	}
 }

 function doFoo(Foo $foo): void
 {
-	$foo->value = 5;
+	$foo->setValue(5);
 }

Or change the property's write visibility if external writes are intended:

 <?php declare(strict_types = 1);

 class Foo
 {
-	public private(set) int $value = 0;
+	public int $value = 0;
 }

 function doFoo(Foo $foo): void
 {
 	$foo->value = 5;
 }