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Error Identifier: function.alreadyNarrowedType

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 process(int $value): void
{
	if (is_int($value)) {
		echo $value;
	}
}

Why is it reported? #

A type-checking function call will always evaluate to true because the type of the argument has already been narrowed to match the check. This means the condition is redundant – the type is already guaranteed by a previous check, a type declaration, or the control flow.

In the example above, $value is declared as int, so is_int($value) is always true.

How to fix it #

Remove the unnecessary type check when the type is already guaranteed by the parameter type:

 <?php declare(strict_types = 1);
 
 function process(int $value): void
 {
-	if (is_int($value)) {
-		echo $value;
-	}
+	echo $value;
 }

If the function accepts a union type, the check may become meaningful:

 <?php declare(strict_types = 1);
 
-function process(int $value): void
+function process(int|string $value): void
 {
 	if (is_int($value)) {
 		echo $value;
 	}
 }

How to ignore this error #

You can use the identifier function.alreadyNarrowedType to ignore this error using a comment:

// @phpstan-ignore function.alreadyNarrowedType
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: function.alreadyNarrowedType

Rules that report this error #

• PHPStan\Rules\Comparison\ImpossibleCheckTypeFunctionCallRule [1]

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