Cannot use [] for reading

Description

The append operator [] is a write operator: it alters the underlying variable. It cannot be used for reading, as it doesn’t produce a value. Hence, it is not possible to use the append operator as an argument, or with a short assignement operator.

Example

<?php

// += needs a value to increment, which [] cannot provide
$a[] += 2;

// When foo() is called, the value of the arguments is transmitted to the function.
// Here, $a[] has no value.
foo($a[]);

?>

Solutions

• Only use [] in writing context.