Adding function at run time in PHP classes [duplicate]

I have class

class a{
     var $test;
}

I have lots of functions in files. Each file having its own function like

File1.php contains function File1(){}

There are 50+ files for function. I want to dynamically add onliy one function at runtime, So that final class structure like this

class a{
var $test;
function File1(){
}
}