From: Robert Klemme <shortcutter@...>
Date: 2013-04-30T00:29:46+09:00
Subject: Re: New Rexx like data structure

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On Mon, Apr 29, 2013 at 5:07 PM, Peter Hickman <
peterhickman386@googlemail.com> wrote:

> This is just something that I have been playing with for some time but I
> thought a structure like this might be cool.
>
> a = Hash.new
> a.b = 12
>
> This behaves the same as a['b'] = 12, and this ...
>
> a.c.d = 42
>
> behaves like this ...
>
> a['c']['d'] = 42
>
> The syntax looks cleaner to me if a little Rexxish (or Lua like). Here's
> how I implemented it
>
> class Hash
>   def method_missing(m, *args, &block)
>     key = m.to_s
>
>     if key =~ /(.*)=$/
>       self.store($1, args.first)
>     elsif self[key] == nil
>       self.store(key, Hash.new)
>     else
>       self[key]
>     end
>   end
> end
>
> There is just one little wrinkle in this plan
>
> a.j => Hash
>
> Given that a.j has not beed defined, that is there has been no "a.j = 19"
> for example, I would prefer that a.j return nil but can't for the life of
> me think how to get this to work.
>

There is no way because a getter method cannot know whether the result is
used as is or whether it is part of a chain and another setter is invoked.
 In other words:

x = a.c # case 1
a.c.d = 9 # case 2

Here, no implementation of method c can detect whether we have case 1 or 2.

This reminds me of OpenStruct...

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

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<div dir=3D"ltr"><br><div class=3D"gmail_extra"><br><br><div class=3D"gmail=
_quote">On Mon, Apr 29, 2013 at 5:07 PM, Peter Hickman <span dir=3D"ltr">&l=
t;<a href=3D"mailto:peterhickman386@googlemail.com" target=3D"_blank">peter=
hickman386@googlemail.com</a>&gt;</span> wrote:<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex"><div dir=3D"ltr">This is just something that=
 I have been playing with for some time but I thought a structure like this=
 might be cool.<div>
<br></div><div><div>a =3D Hash.new</div><div>a.b =3D 12</div><div><br></div=
><div>
This behaves the same as a[&#39;b&#39;] =3D 12, and this ...</div><div><br>=
</div><div>a.c.d =3D 42<br></div><div><br></div><div>behaves like this ...<=
/div><div><br></div><div>a[&#39;c&#39;][&#39;d&#39;] =3D 42</div>
<div><br></div><div>The syntax looks cleaner to me if a little Rexxish (or =
Lua like). Here&#39;s how I implemented it</div><div><br></div><div><div>cl=
ass Hash</div><div>=A0 def method_missing(m, *args, &amp;block)</div>
<div>=A0 =A0 key =3D m.to_s</div><div><br></div><div>=A0 =A0 if key =3D~ /(=
.*)=3D$/</div><div>=A0 =A0 =A0 self.store($1, args.first)</div><div>=A0 =A0=
 elsif self[key] =3D=3D nil</div><div>=A0 =A0 =A0 self.store(key, Hash.new)=
</div><div>=A0 =A0 else</div><div>

=A0 =A0 =A0 self[key]</div><div>=A0 =A0 end</div><div>=A0 end =A0</div><div=
>end</div><div><br></div><div>There is just one little wrinkle in this plan=
</div><div><br></div><div>a.j =3D&gt; Hash</div><div><br></div>
<div>Given that a.j has not beed defined, that is there has been no &quot;a=
.j =3D 19&quot; for example, I would prefer that a.j return nil but can&#39=
;t for the life of me think how to get this to work.</div></div></div></div=
>
</blockquote></div><div class=3D"gmail_extra"><br></div>There is no way bec=
ause a getter method cannot know whether the result is used as is or whethe=
r it is part of a chain and another setter is invoked. =A0In other words:</=
div>
<div class=3D"gmail_extra"><br></div><div class=3D"gmail_extra">x =3D a.c #=
 case 1</div><div class=3D"gmail_extra">a.c.d =3D 9 # case 2</div><div clas=
s=3D"gmail_extra"><br></div><div class=3D"gmail_extra">Here, no implementat=
ion of method c can detect whether we have case 1 or 2.</div>
<div class=3D"gmail_extra"><br></div><div class=3D"gmail_extra">This remind=
s me of OpenStruct...<br><br>Kind regards</div><div class=3D"gmail_extra"><=
br></div><div class=3D"gmail_extra">robert<br clear=3D"all"><div><br></div>=
-- <br>
remember.guy do |as, often| as.you_can - without end<br><a href=3D"http://b=
log.rubybestpractices.com/">http://blog.rubybestpractices.com/</a>
</div></div>

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