From: Anton Bangratz <tony@...>
Date: 2010-10-28T19:02:09+09:00
Subject: Re: ctype functionality without a gem?

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On 10/28/2010 11:16 AM, Ammar Ali wrote:
> On Thu, Oct 28, 2010 at 11:47 AM, Robert Klemme
> <shortcutter@googlemail.com> wrote:
>> On Thu, Oct 28, 2010 at 9:50 AM, Ammar Ali <ammarabuali@gmail.com> wro=
te:
>>> Is there a built-in method for identifying character types a la
>>> ctype() in C? I would like to avoid requiring a gem dependency.
>=20
>> What do you need that for?  Why not directly use a regexp to match a
>> string?  Often you can use capturing groups in a single regexp, e.g.
>>
>> irb(main):009:0> %w{foo bar 123}.each do |s|
>> irb(main):010:1* if /(\d+)|(\w+)/ =3D~ s
>> irb(main):011:2> puts "number" if $1
>> irb(main):012:2> puts "chars" if $2
>> irb(main):013:2> end
>> irb(main):014:1> end
>> chars
>> chars
>> number
>> =3D> ["foo", "bar", "123"]
>=20
> That's very cool. I'll have to remember that one.

It is a bit brittle, though. Watch:

 %w{foo bar 123 345bar}.each do |s|
   if /(\d+)|(\w+)/ =3D~ s
     puts "number" if $1
     puts "chars" if $2
   end
 end
#=3D>
chars
chars
number
number

>=20
> I do actually need to test if a character is of a certain type, all by
> itself, as part of a parser I'm working on. I came up with this quick
> solution for now, http://gist.github.com/650968
>=20
> Thanks,
> Ammar
>=20
>=20

This is similarily fragile. If you are only testing for one character,
it seems good, if you are going to test for strings, it will not be
enough.

Also, the whole solution is not necessarily fast - I do love regular
expressions, but I would search on for other methods to meet your
requirements. It really depends on what your goal is. If it is about
bit streams, you might want to look into bit-struct or similar
approaches that use Array#pack and String#unpack.

Regards,

t.

--=20
Anton Bangratz - Key ID 363474D1 - http://tony.twincode.net/
fortune(6):
If I love you, what business is it of yours?
		-- Johann van Goethe


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