Error Identifier: impure.new

← Back to impure.*

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 Logger
{
	/** @phpstan-impure */
	public function __construct()
	{
		echo 'Logger initialized';
	}
}

/**
 * @phpstan-pure
 */
function createLogger(): Logger
{
	return new Logger();
}

Why is it reported? #

A function or method marked as @phpstan-pure must not have side effects and must always return the same result for the same inputs. Instantiating a class with new is considered impure when the constructor is known to have side effects (such as writing to a file, echoing output, or modifying global state). PHPStan reports this when the constructor is explicitly marked as @phpstan-impure.

How to fix it #

If the class constructor is truly side-effect-free, mark it as @phpstan-pure:

 <?php declare(strict_types = 1);
 
 class Logger
 {
-	/** @phpstan-impure */
+	/** @phpstan-pure */
 	public function __construct()
 	{
-		echo 'Logger initialized';
+		// no side effects
 	}
 }

Or remove the @phpstan-pure annotation from the calling function if it genuinely needs to create objects with impure constructors:

 <?php declare(strict_types = 1);
 
-/**
- * @phpstan-pure
- */
 function createLogger(): Logger
 {
 	return new Logger();
 }

How to ignore this error #

You can use the identifier impure.new to ignore this error using a comment:

// @phpstan-ignore impure.new
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: impure.new

Rules that report this error #

• PHPStan\Rules\Pure\PureFunctionRule [1]
• PHPStan\Rules\Pure\PureMethodRule [1]