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Error Identifier: function.impossibleType

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 doFoo(string $value): void
{
	if (is_int($value)) {
		// ...
	}
}

Why is it reported? #

A type-checking function call will always evaluate to false because the checked type is incompatible with the variable’s type. In the example above, $value is typed as string, so is_int($value) can never be true. This usually indicates a logic error or an incorrect type declaration.

How to fix it #

Fix the type declaration to match the actual range of values, or fix the type check:

-function doFoo(string $value): void
+function doFoo(string|int $value): void
 {
 	if (is_int($value)) {
 		// ...
 	}
 }

Or fix the condition to check for the correct type:

 function doFoo(string $value): void
 {
-	if (is_int($value)) {
+	if (is_numeric($value)) {
 		// ...
 	}
 }

How to ignore this error #

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

// @phpstan-ignore function.impossibleType
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.impossibleType

Rules that report this error #

• PHPStan\Rules\Comparison\ImpossibleCheckTypeFunctionCallRule [1]

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