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Error Identifier: pipe.byRef

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);

function modify(string &$s): void
{
	$s = strtoupper($s);
}

$result = 'hello' |> modify(...);

Why is it reported? #

The pipe operator |> passes the left-hand side as the first argument to the callable on the right. This value is passed by value, not by reference. When the callable declares its first parameter as pass-by-reference (&), the pipe operator cannot fulfil that contract, so PHPStan reports an error.

How to fix it #

Change the callable to accept its first parameter by value instead of by reference, and return the result:

 <?php declare(strict_types = 1);
 
-function modify(string &$s): void
+function modify(string $s): string
 {
-	$s = strtoupper($s);
+	return strtoupper($s);
 }

 $result = 'hello' |> modify(...);

How to ignore this error #

You can use the identifier pipe.byRef to ignore this error using a comment:

// @phpstan-ignore pipe.byRef
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: pipe.byRef

Rules that report this error #

• PHPStan\Rules\Operators\PipeOperatorRule [1]

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