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From Mark Slee <ms...@facebook.com>
Subject RE: optional fields in function declaration
Date Wed, 01 Jul 2009 20:46:26 GMT
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:jamspam@jobstick.com] 
Sent: Wednesday, July 01, 2009 1:42 PM
To: thrift-user@incubator.apache.org
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:matthieu.imbert@ens-lyon.fr] 
> Sent: Wednesday, July 01, 2009 11:14 AM
> To: thrift-user@incubator.apache.org
> 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.
> 


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