1.2.888. Only Variable Passed By Reference

Some methods require a variable as argument. Those arguments are passed by reference, and they must operate on a variable, or any data container (property, array element).

This means that literal values, constants cannot be used as argument. This is also the case of literal values, returned by other methods.

This is also the case of isset(), althought with a different error message.

<?php

echo end([1,2,3]);

function foo() {
     return [4,5,6];
}

echo end(foo());

?>