Error Identifier: array.unusedOffset

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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 mixed $v */
function sink($v): void
{
}

function doFoo(): void
{
	$a = ['x' => 1, 'y' => 2];
	sink($a['y']);
}

Why is it reported? #

The array assigned to $a stores a value under offset 'x', but only offset 'y' is ever read back from $a. The value under 'x' is a dead store: it is computed and kept, but no code observes it.

Unlike variable.unused, the array $a itself is used; only this particular offset is redundant. A dead offset often points to a leftover key or a logic error, such as reading the wrong offset name.

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 #

Remove the offset whose value is never read:

 function doFoo(): void
 {
-	$a = ['x' => 1, 'y' => 2];
+	$a = ['y' => 2];
 	sink($a['y']);
 }

Or read the offset if it was intended to be used:

 function doFoo(): void
 {
 	$a = ['x' => 1, 'y' => 2];
+	sink($a['x']);
 	sink($a['y']);
 }

How to ignore this error #

You can use the identifier array.unusedOffset to ignore this error using a comment:

// @phpstan-ignore array.unusedOffset
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: array.unusedOffset

Rules that report this error #

• PHPStan\Rules\DeadCode\UnusedVariableRule [1]