assignOp.invalid

Code example

<?php declare(strict_types = 1);

$a = 'hello';
$a -= 5;

Why is it reported?

The compound assignment operator (such as +=, -=, *=, .=, etc.) cannot be applied to the given combination of types. The operation between the left-hand variable and the right-hand value produces a type error.

In the example above, the -= operator is applied between a string and an int, which is not a valid binary operation.

How to fix it

Ensure the variable and the value are compatible types for the operation:

 <?php declare(strict_types = 1);

-$a = 'hello';
-$a -= 5;
+$a = 10;
+$a -= 5;

Or use the correct operator for the types involved:

 <?php declare(strict_types = 1);

 $a = 'hello';
-$a -= 5;
+$a .= ' world';