possiblyImpure.echo

Code example

<?php declare(strict_types = 1);

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

Why is it reported?

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

The function or method is marked as @phpstan-pure, but it contains an echo statement. Pure functions must not have side effects -- they should only compute and return a value based on their input parameters. Outputting text with echo is a side effect because it modifies the program's output stream.

How to fix it

Remove the echo statement from the pure function and let the caller handle the output:

 <?php declare(strict_types = 1);

 /** @phpstan-pure */
 function formatAndPrint(string $name): string
 {
 	$result = 'Hello, ' . $name;
-	echo $result;
 	return $result;
 }
+
+echo formatAndPrint('World');

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

 <?php declare(strict_types = 1);

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