PHP表达式返回值和变量之间的差异

Question

Why does it make a difference if a function's return value (a variable) is passed and not a variable directly? In the PHP documentation for the empty() function it is stated that

5.5.0: empty() now supports expressions, rather than only variables.

But why would that make a difference anyway? If the given expression has a variable as a return value - in my eyes - both statements would be exactly the same.

Answer 1

Prior to PHP 5.5, the returned value is a value, not a variable because when you say

return $value;

in your called function, $value is only valid in the scope of the function; it ceases to exist as a variable as soon as the function terminates its execution, so the calling code only receives the value