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psalm/docs/running_psalm/issues/MixedOperand.md
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# MixedOperand
Emitted when Psalm cannot infer a type for an operand in any calculated expression
```php
<?php
echo $_GET['foo'] + "hello";
```
## Why its bad
Mixed operands can have fatal consequences, e.g. here:
```php
<?php
function foo(mixed $m) {
echo $m . 'bar';
}
class A {}
foo(new A()); // triggers fatal error
```