On Saturday, 13 October 2012 at 11:50:40 UTC, Maxim Fomin wrote:
I think implementing UFCS operator overloading is problematic. Firstly, you want to put this language addition too far.
I don't see this as taking UFCS functionality "further". Rather, I think it's simply more logical that with UFCS you could provide extra operator methods just like you can provide extra "regular" methods. I assumed that UFCS operator overloading would work for sure, and it seems arbitrary to me that it doesn't.
Secondly, compiler needs to know whether operator was overloaded or not. If it knows, it generates code to call "opSomething", if nor - it just doesn't generate anything. Now, imagine what would happen if you write in some module "free" function, supposed to hijack operator overloading method of class or struct in another module. If you compile them together, operator would be overloaded, if separately - nothing would happen. This means that operator overloading would depend on with what you compile your module - sometimes nothing would be overloaded, sometimes it would be with one function, sometimes with another.
You use the word "hijack", but free functions can't hijack anything. They can only provide new functionality. The situation you describe is exactly parallel to using UFCS (with regular functions) like this:
//File: mystruct.d module mystruct; struct MyStruct { int _value; } //File: incr1.d module incr1; import mystruct; void incr(ref MyStruct ms) { ms._value += 1; } //File: incr2.d module incr2; import mystruct; void incr(ref MyStruct ms) { ms._value += 2; } //File: main.d module main; import std.stdio; import mystruct; static if (true) // change to false to print "2" import incr1; else import incr2; void main() { MyStruct ms; ms.incr(); writeln(ms._value); // prints "1" }
Thirdly, I see no reason in allowing it - for what purpose does you proposal service for?
The main reason to me is that it would make more sense. It'd seem more logical that way. I can't think of any use cases.