From: Eric Mahurin <eric_mahurin@...>
Date: 2005-07-20T03:32:02+09:00
Subject: RCR: required args after optional ones (was Re: [RCR] nil for unassigned keys)

--- Daniel Brockman <daniel@brockman.se> wrote:

> Hi Eric,
> 
> > I thought you were going to submit an RCR for this (not
> > too related to the original RCR topic of this thread - nil
> > for unassigned keys - of a hash).
> 
> I know, I'm sorry.  As I said earlier in this thread,
> 
> Myself> That reminds me, I promised I would write an RCR for
> Myself> allowing trailing argument after the splatting one.
> 
> Myself> It was said that optional arguments should be
> Myself> allowed before the splat, but not after it.
> 
> Eric, what is your opinion on this?  Do you think these
> 
>    def foo(a, b=nil, c, d=nil, e) ... end

don't like it - too ambiguous.  Does b or d get assigned when
you have 4 args?

>    def bar(a, b=nil, *c, d=nil, e) ... end

also don't like it - too ambiguous.  Does b or d get assigned
when you have 3 args?

>    def baz(*a, b=nil, c=nil) ... end

maybe.  you could handle this if optional args have priority
over splats.

> should all be allowed?
> 
> If so, then which variable, b or c, should be bound when
> invoking baz with one argument?  The obvious answer is b,
> but you could argue that c makes more sense, since c is
> farthest from the splat.

I was thinking c to be symmetrical with optionals coming before
the splat.


I think the meat of this RCR should handle these cases:

def f(a, b, c=c0, d=d0, y, z) ... end

def f(a, b, *m, y, z) ... end

def f(a, b, c=c0, d=d0, *m, y, z) ... end

I think these are pretty clear: y and z get the last 2 args and
the rest of the args are handled as they are now.  I think this
would be a bit more controversial:

def f(a, b, *m, w=w0, x=x0, y, z) ... end

In this case, after grabbing a, b, y, and z from the args, x
would have priority over w and w over m.  That would be
symmetrical with optional args coming before the splat, but
confusing.  Especially when you might be confused as to whether
w or x should have priority (as you discussed above).

What case do you have where you want optional args after the
splat?


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