在PHP中编写OR条件时出现奇怪的错误

Question

This error has been bugging me for a long time and I can't find an answer anywhere on the Internet, even using PHP official documentation.

When I write if statements with multiple conditions like this

if ((empty($user) == true) || (isset($user->data) == false)) {
    //...
}

PHP says "Call to undefined function ()".

Then I try this alternative:

if (empty($user) == true || isset($user->data) == false) {
    //...
}

And PHP says Call to undefined function isset().

PHP version 5.5.15.

Answer 1

How about:

if (empty($user) || !isset($user->data)) {
    //...
}