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Error Identifier: impure.print

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);

/** @phpstan-pure */
function formatAndPrint(string $name): int
{
	return print 'Hello, ' . $name;
}

Why is it reported? #

The print language construct is used inside a function or method marked as @phpstan-pure. Pure functions must not have side effects – they should only compute and return a value based on their inputs. Using print outputs text to the standard output, which is a side effect.

How to fix it #

Remove the print call from the pure function and return the formatted string instead:

 <?php declare(strict_types = 1);
 
 /** @phpstan-pure */
-function formatAndPrint(string $name): int
+function format(string $name): string
 {
-	return print 'Hello, ' . $name;
+	return 'Hello, ' . $name;
 }

Or remove the purity annotation if the function genuinely needs to produce output:

 <?php declare(strict_types = 1);
 
-/** @phpstan-pure */
 function formatAndPrint(string $name): int
 {
 	return print 'Hello, ' . $name;
 }

How to ignore this error #

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

// @phpstan-ignore impure.print
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.print

Rules that report this error #

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

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