difference between function and &function [duplicate]

Question

function fun1();
function &fun1();

What is the difference between these??

Answer 1

If you put an ampersand before your function name, the function will return a reference to a variable instead of the value.

Returning by reference is useful when you want to use a function to find to which variable a reference should be bound. Do not use return-by-reference to increase performance. The engine will automatically optimize this on its own. Only return references when you have a valid technical reason to do so.

From the PHP Manual on Returning References.