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Error Identifier: phpstanApi.instanceofAssumption

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);

use PHPStan\Type\Type;
use PHPStan\Type\StringType;

function doFoo(Type $type): void
{
	if ($type instanceof StringType) { // ERROR: Although StringType is covered by backward compatibility promise, this instanceof assumption might break because it's not guaranteed to always stay the same.
		// ...
	}
}

Why is it reported? #

This error is reported when an instanceof check is used against a PHPStan class that is covered by the backward compatibility promise, but the specific instanceof assumption might break in a future minor version. While the class itself is part of the public API, PHPStan does not guarantee that a value currently represented by a specific class will always be represented by that same class.

For example, a type that is currently a StringType instance might be represented differently in a future version, even though the StringType class itself still exists.

How to fix it #

Instead of checking for a specific class with instanceof, use the type’s API methods to query its properties:

 <?php declare(strict_types = 1);
 
 use PHPStan\Type\Type;
-use PHPStan\Type\StringType;

 function doFoo(Type $type): void
 {
-	if ($type instanceof StringType) {
+	if ($type->isString()->yes()) {
 		// ...
 	}
 }

If you believe the instanceof check is the correct approach and should be supported, open a discussion at github.com/phpstan/phpstan/discussions.

See also: Backward Compatibility Promise

How to ignore this error #

You can use the identifier phpstanApi.instanceofAssumption to ignore this error using a comment:

// @phpstan-ignore phpstanApi.instanceofAssumption
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: phpstanApi.instanceofAssumption

Rules that report this error #

• PHPStan\Rules\Api\ApiInstanceofRule [1]

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