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Error Identifier: property.readOnlyDefaultValue

Every error reported by PHPStan has an error identifier. Here’s a list of all error identifiers. In PHPStan Pro you can see the error identifier next to each error and filter errors by their identifiers.

Code example #

<?php declare(strict_types = 1);

class Config
{

	public readonly string $name = 'default';

}

Why is it reported? #

A readonly property cannot have a default value. PHP does not allow readonly properties to be initialized with a default value in their declaration because a readonly property can only be written once, and that write must happen explicitly (typically in the constructor). Allowing a default value would conflict with the semantics of readonly, which guarantees the property is initialized at a single point in code.

How to fix it #

Move the initialization to the constructor:

 <?php declare(strict_types = 1);
 
 class Config
 {

-	public readonly string $name = 'default';
+	public readonly string $name;
+
+	public function __construct()
+	{
+		$this->name = 'default';
+	}

 }

Or use a promoted constructor parameter:

 <?php declare(strict_types = 1);
 
 class Config
 {

-	public readonly string $name = 'default';
-
+	public function __construct(
+		public readonly string $name = 'default',
+	)
+	{
+	}

 }

How to ignore this error #

You can use the identifier property.readOnlyDefaultValue to ignore this error using a comment:

// @phpstan-ignore property.readOnlyDefaultValue
codeThatProducesTheError();

You can also use only the identifier key to ignore all errors of the same type in your configuration file in the ignoreErrors parameter:

parameters:
	ignoreErrors:
		-
			identifier: property.readOnlyDefaultValue

Rules that report this error #

• PHPStan\Rules\Properties\ReadOnlyPropertyRule [1]

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