Yeah, but things get pretty messy when you have three parameters (or any situation of multiple optional params with the same type).
void function foo(int a, int b, int c) void function foo(int a, int b) void function foo(int a, int c) <= NO THANKS! Already declared a function foo with 2-int params. Also gets messy if you decide to add/remove/reorder the params to your function. Now you've got to go update all the calls to helpers in your application code. Easier to just be explicit here. -----Original Message----- From: Jonathan Marcus [mailto:[email protected]] Sent: Wednesday, July 01, 2009 1:42 PM To: [email protected] Subject: Re: optional fields in function declaration Nonetheless, it should be fairly easy to implement optional parameters across languages, using method overloading in those languages that don't directly support optional parameters. Thrift: void function foo(1:i32 a, 2:i32 b = -1) C#/Java: public void foo(int a) { foo(a, -1); } public void foo(int a, int b) PHP: public function foo($a, $b = -1) You are correct about it being impossible to disambiguate a default-value from one not set, but aside from that this should work in every language. --Jonathan Mark Slee wrote: > Yeah there's really no way to do this in most languages that don't support > variable args. For instance, consider C++ and Java > > void myMethod(int x) > > There's just no way to make x optional. An integer variable x simply MUST be > passed into this function. You can provide a default value if you like and > not set it yourself, but there's no getting around the argument being present. > > If your application needs to disambiguate between a default-value and absence > of an argument, then you must use a struct and inspect the isset field > directly. > > -----Original Message----- > From: Matthieu Imbert [mailto:[email protected]] > Sent: Wednesday, July 01, 2009 11:14 AM > To: [email protected] > Subject: Re: optional fields in function declaration > > Bryan Duxbury wrote: >> I would say that there's no question it would be useful. However, I'm >> not sure how that would translate to all client languages. >> >> A completely safe and reliable way to simulate this would be to make a >> new struct for your method that has optional fields and just use that as >> the only parameter to the method. Does that make sense? > > Yes, i'm already doing this and it works great. The only two drawbacks > is that you end up with a lot of structs if you have lots of functions > with optional parameters, and of course the client API is not as simple > and straightforward to use. >
