Cannot use temporary expression in write context

Description

Literal values and constants cannot be used with the append operator. Those values must be placed in a container, such as a variable, array element, property. That way, they become updatable, and can be appended.

The literal values may be hidden in a returned value, or by a call to native PHP functions which return literals.

Passing a dimension fetch on a temporary by reference is also not allowed.

Example

<?php

// Attempt to append 1 to an empty literal array
[][] = 1;
array()[] = 1;

$a = array();
$a[] = 1;

$fn = function(&$ref) {};
$fn([0, 1][0]);

function goo() { return [0, 1][0];}
// The constant is hidden in the function goo()
$fn(goo());

function hoo($fn) {
     // PHP provide literal values
     $fn(func_get_args()[0]);
}


?>

Solutions

• Store the literal value in a variable before use it with append.