If you have a callback that is going to be invoked often, you can use this method (and the related method for ReflectProperty) to get a closure that will execute at near native speed.Some benchmark comparisons with php 5.4.22 on ubuntu:[function call] [time] [%slower]function(): 0.09527 0%Reflection::Closure: 0.09729 2%$string(): 0.102641 8%Reflection: 0.197122 107%call_user_func: 0.214045 125%[method call] [time] [% slower] [%vs func]->method(): 0.103611 0% 9%Reflection::Closure: 0.1043 1% 9%$string(): 0.109885 6% 15%Reflection: 0.20451 97% 115%call_user_func: 0.219205 112% 130%