From: Joshua Ballanco <jballanc@...>
Date: 2011-10-27T04:03:52+09:00
Subject: [ruby-core:40418] Re: [ruby-trunk - Feature #5474][Assigned] keyword argument

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On Wed, Oct 26, 2011 at 2:08 PM, Yukihiro Matsumoto <matz@ruby-lang.org>wrote:

> Hi,
>
> In message "Re: [ruby-core:40414] Re: [ruby-trunk - Feature
> #5474][Assigned] keyword argument"
>     on Thu, 27 Oct 2011 02:51:51 +0900, Charles Oliver Nutter <
> headius@headius.com> writes:
>
> |Evan and I would like to see support for non-default keyword args. So
> |the following form would require that "size" be provided as a keyword
> |arg, and otherwise raise an ArgumentError:
> |
> |def create_point(x, y, color: "white", size:)
>
> I don't know the reason why you need this value-less keyword
> argument.  If you want the default value, you just need to omit the
> keyword altogether.
>

I think the point is that not every argument necessarily has a reasonable
default. Imagine, for example, if we were to rewrite File.open to take
keyword arguments:

    class File
      def self.open(filename:, mode: 'r')
      ...

It would be desirable to call such a method as `File.open(filename:
"foo.txt")` but omitting the "filename:" argument should be an error.
Perhaps, if a hash-like syntax is desired, we could introduce a "required"
keyword:

    class File
      def self.open(filename: required, mode: 'r')
      ...

such that omitting the option raises an ArgumentError?

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<br><div class=3D"gmail_quote">On Wed, Oct 26, 2011 at 2:08 PM, Yukihiro Ma=
tsumoto <span dir=3D"ltr">&lt;<a href=3D"mailto:matz@ruby-lang.org">matz@ru=
by-lang.org</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote" styl=
e=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
Hi,<br>
<br>
In message &quot;Re: [ruby-core:40414] Re: [ruby-trunk - Feature #5474][Ass=
igned] keyword argument&quot;<br>
<div class=3D"im"> =C2=A0 =C2=A0on Thu, 27 Oct 2011 02:51:51 +0900, Charles=
 Oliver Nutter &lt;<a href=3D"mailto:headius@headius.com">headius@headius.c=
om</a>&gt; writes:<br>
<br>
|Evan and I would like to see support for non-default keyword args. So<br>
|the following form would require that &quot;size&quot; be provided as a ke=
yword<br>
|arg, and otherwise raise an ArgumentError:<br>
|<br>
|def create_point(x, y, color: &quot;white&quot;, size:)<br>
<br>
</div>I don&#39;t know the reason why you need this value-less keyword<br>
argument. =C2=A0If you want the default value, you just need to omit the<br=
>
keyword altogether.<br></blockquote><div><br></div><div>I think the point i=
s that not every argument necessarily has a reasonable default. Imagine, fo=
r example, if we were to rewrite File.open to take keyword arguments:</div>
<div><br></div><div>=C2=A0 =C2=A0 class File</div><div>=C2=A0 =C2=A0 =C2=A0=
 def self.open(filename:, mode: &#39;r&#39;)</div><div>=C2=A0 =C2=A0 =C2=A0=
 ...</div><div><br></div><div>It would be desirable to call such a method a=
s `File.open(filename: &quot;foo.txt&quot;)` but omitting the &quot;filenam=
e:&quot; argument should be an error. Perhaps, if a hash-like syntax is des=
ired, we could introduce a &quot;required&quot; keyword:</div>
<div><br></div><div>=C2=A0 =C2=A0 class File</div><div>=C2=A0 =C2=A0 =C2=A0=
 def self.open(filename: required, mode: &#39;r&#39;)</div><div>=C2=A0 =C2=
=A0 =C2=A0 ...</div><div><br></div><div>such that omitting the option raise=
s an ArgumentError?=C2=A0</div></div>

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