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psalm/docs/running_psalm/issues/NoValue.md

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# NoValue
Emitted when Psalm invalidated all possible types for a given expression. It is often an indication that Psalm found dead code or that documented types were not exhaustive
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```php
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<?php
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/**
* @return never
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*/
function foo() : void {
exit();
}
$a = foo(); // Psalm knows $a will never contain any type because foo() won't return
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```
```php
<?php
function foo() : void {
return throw new Exception(''); //Psalm detected the return expression is never used
}
```
```php
<?php
function shutdown(): never {die('Application closed unexpectedly');}
function foo(string $_a): void{}
foo(shutdown()); // foo() will never be called
```
```php
<?php
$a = [];
/** @psalm-suppress TypeDoesNotContainType */
assert(!empty($a));
count($a); // Assert above always fail. There is no possible type that $a can have here
```