From: Xavier Noria <fxn@...>
Date: 2012-03-22T06:11:30+09:00
Subject: Re: What’s the best way to check if a feature/class has been loaded?

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On Wed, Mar 21, 2012 at 9:51 PM, Nikolai Weibull <now@bitwi.se> wrote:

There=E2=80=99s a timing issue with using const_defined? followed by const_=
get
> instead of calling const_get directly and catching NameError.


What do you mean?

The problem with const_get is that it follows the ancestors, of course, and
you have no way around that in 1.8.


I guess
>
> def feature?(path)
>   path.split('::').reduce(Object){ |o, e|
>      c =3D begin o.const_get(e); rescue NameError; return nil end
>     return nil if c =3D=3D (o !=3D Object and begin Object.const_get(e);
> rescue NameError; nil end)
>     c
>   }
> end


Nikolai, I don't really understand what you need. You are askind for
defined? X::Y that goes step by step and your original code does raise an
error for X::Y integer.

Then this second version cannot say that X::Y is defined in

    module X
      Y =3D nil
   end

And you refuse to reuse much more simple and proven existing solutions.

You want something with so special semantics that definitely is NOT
built-in. That answers you original question.

Good luck!

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On Wed, Mar 21, 2012 at 9:51 PM, Nikolai Weibull <span dir=3D"ltr">&lt;<a h=
ref=3D"mailto:now@bitwi.se" target=3D"_blank">now@bitwi.se</a>&gt;</span> w=
rote:<div><br><div><div class=3D"gmail_quote"><blockquote class=3D"gmail_qu=
ote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex=
">



There=E2=80=99s a timing issue with using const_defined? followed by const_=
get<br>
instead of calling const_get directly and catching NameError.</blockquote><=
div><br></div><div>What do you mean?</div><div><br></div><div>The problem w=
ith const_get is that it follows the ancestors, of course, and you have no =
way around that in 1.8.</div>



<div><br></div><div><br></div><blockquote class=3D"gmail_quote" style=3D"ma=
rgin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
I guess<br>
<div><br>
def feature?(path)<br>
 =C2=A0 path.split(&#39;::&#39;).reduce(Object){ |o, e|<br>
</div> =C2=A0 =C2=A0 c =3D begin o.const_get(e); rescue NameError; return n=
il end<br>
 =C2=A0 =C2=A0 return nil if c =3D=3D (o !=3D Object and begin Object.const=
_get(e);<br>
rescue NameError; nil end)<br>
 =C2=A0 =C2=A0 c<br>
 =C2=A0 }<br>
end</blockquote><div><br></div><div>Nikolai, I don&#39;t really understand =
what you need. You are askind for defined? X::Y that goes step by step and =
your original code does raise an error for X::Y integer.</div><div><br>



</div><div>Then this second version cannot say that X::Y is defined in</div=
><div><br></div><div><div>=C2=A0 =C2=A0 module X</div><div>=C2=A0 =C2=A0 =
=C2=A0 Y =3D nil</div><div>=C2=A0 =C2=A0end</div></div><div><br></div><div>=
And you refuse to reuse much more simple and proven existing solutions.</di=
v>



<div><br></div><div>You want something with so special semantics that defin=
itely is NOT built-in. That answers you original question.</div><div><br></=
div><div>Good luck!</div><div><br></div></div></div></div>

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