On 2011-05-27 08:34, Matthew Ong wrote:
Hi All,Currently within D, to make use of a parent class method you have to do: class Parent{ void methodA(int x){...} } class Child : Parent{ // I understand that it has to do with preventing accidental hijacking alias Parent.methodA methodA; void methodA(long x){...} } void main(string[]){ Child obj=new Child(); obj.methodA(1); // expecting to call Child.methodA but calling Parent.methodA; } and also from this URL. http://www.digitalmars.com/d/2.0/function.html If, through implicit conversions to the base class, those other functions do get called, an std.HiddenFuncError exception is raised. ----------------------------------------------------------------------- That is to prevent silently changing the program's behavior. b.foo(1) could happily be a call to B.foo(long) today. Imagine one of the base classes changed and now there is A.foo(int). Then our b.foo(1) would silently start calling that new function. That would cause a tough bug. Ali // a Better explanation than the document for the current syntax. ------------------------------------------------------------------------ However, there is a foreseeable problem coming when a program grow. How about when the inheritance tree becomes deeper than 4? And more and more overloaded functions are in different classes? That does not meant the calling class/method has a sense if it is calling from Child or Parent. Because, those 2 classes source code might not be available for coder. How does the coder knows about that? Does it mean we have to do more alias at child class at the bottom? Harder to issues solve in the child class at the bottom of the tree. It seem to me that the entire purpose is just to protect auto promotion matching method signature in the base to avoid function hijacking. How about doing this another way? Just a suggestion if you like to avoid parent function from accidental hijack but still needs to be public. New keywords are needed: nooverload and inheritall class Parent{ nooverload void methodA(int x){...} // entirely deny this name to be overloaded. } // this would have avoided the aliasing all over child class and still allow child class to see any >public< method of the parent. class Child: inheritall Parent{ // auto inheriting all parent methods except private ones. As per usual also for package/protected... void methodA(long x){...} // compilation error. because nooverload is used at Parent void methodA(string x){...} // compilation error. because nooverload ... etc void methodB(){ methodA(123); // No error now, and the entire hijacking is avoided. } } void main(string[] args){ Child obj=new Child(); obj.methodB(); // no problem obj.methodA(123); // no accidental hijacking...Always use parent class. } Reverse sequence as Ali has shown can also be avoided because if someone does that by adding 'new' methodA in parent where child already has methodA overloaded already without knowledge. Show up in compilation exception for such cases with -w flag on. How about that? Possible solution?
How big is this problem in practice, how often do need overload (NOT override) a method in the subclass that exists in the super class?
-- /Jacob Carlborg
