Error Identifier: foreach.unusedKey

← Back to foreach.*

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);

/**
 * @param array<string, int> $data
 */
function doFoo(array $data): void
{
	foreach ($data as $key => $value) {
		echo $value;
	}
}

Why is it reported? #

The foreach loop binds each element’s key to $key, but the loop body never reads it. Capturing a key that nobody uses is unnecessary. This often means the body should use $key but doesn’t, or the key does not need to be captured at all.

This rule is part of PHPStan’s dead code analysis. It is reported at rule level 4 and above, and is currently part of Bleeding Edge.

How to fix it #

Drop the key from the foreach if only the value is needed:

-	foreach ($data as $key => $value) {
+	foreach ($data as $value) {
 		echo $value;
 	}

Or use the key in the loop body if it was intended to be read:

 	foreach ($data as $key => $value) {
+		echo $key;
 		echo $value;
 	}

If you deliberately want to keep the key variable, prefix its name with an underscore. PHPStan ignores variables whose name starts with _:

-	foreach ($data as $key => $value) {
+	foreach ($data as $_key => $value) {
 		echo $value;
 	}

How to ignore this error #

You can use the identifier foreach.unusedKey to ignore this error using a comment:

// @phpstan-ignore foreach.unusedKey
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: foreach.unusedKey

Rules that report this error #

• PHPStan\Rules\DeadCode\UnusedVariableRule [1]