From: Gavin Kistner <gavin@...>
Date: 2005-06-13T01:27:07+09:00
Subject: Re: Only if the object exists

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On Jun 12, 2005, at 9:40 AM, Robert Klemme wrote:
> Why change the parser if there are ways to do this that don't =20
> require such heavy language modifications?

I suppose because it seems to me that the only reason that:

    tmp.bar if tmp=3Dfoo

fails to work is a slight naivet=E9 by the parser. I expected it to =20
work, as there is no semantic difference between that and the code:

   if tmp=3Dfoo
       tmp.bar
   end

That it does not work is consistent, however, with the odd fact that =20
introduction of a line like:

     tmp =3D x if false

may affect the later scope of 'tmp'. I guess that's the real =20
disconnect for me. I'm coming from JavaScript, where the scoping for =20
a variable is not based on a top-down parsing, but is based on =20
whether the 'var' keyword declares the variable as local ANYWHERE in =20
the function. It strikes me as odd that this code:

def foo
     10.times{ i =3D i ? i+1 : 1 }
     puts i =3D i ? i+1 : 1
     10.times{ i =3D i ? i+1 : 1 }
     puts i =3D i ? i+1 : 1
end

results in "1" and "12" being written, instead of "11" and "22".

Ruby is the first language I've seen where the scope of a variable is =20=

not the same throughout the same block. If this is on purpose and/or =20
really cool and useful in situations I haven't considered, then I'll =20
accept "tmp.bar if tmp=3Dfoo" not working as a necessary casualty. But =20=

it seems to me that the variable variable scope may be due to an =20
implementation flaw in the pre-processing of code, not a conscious =20
design decision.

I'm not even proposing the 'massive' undertaking of scanning the =20
entire method for "tmp\s*=3D" outside of any blocks to predetermine if =20=

tmp should be local (though IMO that should be done). I'm simply =20
suggesting that the parser conceptually invert the order of single-=20
line "yyyy if/unless xxxx" to process xxxx first.




> class Dummy
>  def method_missing(*a,&b) self end
> end
> DUMMY =3D Dummy.new
>
> (foo || DUMMY).bar

Interesting!


> Apart from that I'd go with the "and" variant:
>
> tmp =3D foo and tmp.bar

My old self who likes to use boolean guards as inline conditionals =20
would do that. My new self who wants to make code very readable and =20
clear to the casual observer is trying to use the words 'if' and =20
'unless'. (YMMV, but IMHO using booleans as conditionals is cool but =20
non-obvious. I know I've had multiple C++ coders look at my =20
JavaScript code using that syntax and say "...wtf is this? What does =20
that do?")

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