possiblyImpure.print

Code example

<?php declare(strict_types = 1);

class Logger
{

	/** @phpstan-pure */
	public function format(string $message): string
	{
		print $message;

		return '[LOG] ' . $message;
	}

}

Why is it reported?

This identifier is not reported in practice because print is always considered definitely impure, not just possibly impure. PHPStan reports impure.print instead.

The function or method is marked as pure (via @phpstan-pure), but it uses print or echo inside its body. Outputting text is a side effect because it sends data to the output buffer, which modifies external state. This makes the function possibly impure.

A pure function must have no side effects and must return a result based only on its arguments.

How to fix it

Remove the print/echo statement from the pure function:

 <?php declare(strict_types = 1);

 class Logger
 {

 	/** @phpstan-pure */
 	public function format(string $message): string
 	{
-		print $message;
-
 		return '[LOG] ' . $message;
 	}

 }

Alternatively, if the function genuinely needs to produce output, remove the @phpstan-pure annotation:

 <?php declare(strict_types = 1);

 class Logger
 {

-	/** @phpstan-pure */
 	public function format(string $message): string
 	{
 		print $message;

 		return '[LOG] ' . $message;
 	}

 }