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From: Maurizio De Santis on 31 Jul 2010 21:19
Hello!

suppose I want to modify Array.slice() (and consequentially, Array[]) in
order to accept a RegExp as argument, and return values matching the
regular expression. I tried to solve this problem in this way:


class Array

def slice_with_regexp(*args)
puts args
return self.select{ |val| val.to_s =~ args[0] } if args.size == 1
and args[0].is_a?(RegExp)
end

alias_method :slice_without_regexp, :slice
alias_method :slice, :slice_with_regexp

end

arr = %w[a b c]
puts arr.slice(/a/)


but executing this script I get this error:

(?-mix:a)
scripts.rb:8:in `slice_with_regexp': uninitialized constant RegExp
(NameError)
from scripts.rb:17:in `<main>'

Surely I did something wrong, but the very question is: what is the
correct way to get the desired effect (that is:)

arr = %w[a b c]
puts arr[/a/]
=> ["a"]
puts arr.slice(/a/)
=> ["a"]

?
--
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From: James Harrison on 31 Jul 2010 22:24
> return self.select{ |val| val.to_s =~ args[0] } if args.size == 1
> and args[0].is_a?(RegExp)

Try Regexp, not RegExp

http://ruby-doc.org/core/classes/Regexp.html




From: Maurizio De Santis on 1 Aug 2010 05:02
James Harrison wrote:
>> return self.select{ |val| val.to_s =~ args[0] } if args.size == 1
>> and args[0].is_a?(RegExp)
>
> Try Regexp, not RegExp
>
> http://ruby-doc.org/core/classes/Regexp.html

LOL that's what I obtain when I'm still not asleep at 3.00 am :P

But now it's morning, and I have still a problem; please consider this:


class Array

def slice_with_regexp(*args)
return self.select{ |val| val =~ args[0] } if args.size == 1 and
args[0].is_a?(Regexp)
slice_without_regexp(*args)
end

alias_method :slice_without_regexp, :slice
alias_method :slice_without_regexp, :[]
alias_method :slice, :slice_with_regexp

end

arr = %w[a b c ab]
puts arr.slice(/a/).inspect # => ["a", "ab"] slice with Regexp works;
correct
puts arr.slice(1).inspect # => "b" original slice still works; correct
puts arr[/a/].inspect # => stack level too deep ???

why??
--
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From: Brian Candler on 1 Aug 2010 07:20
Maurizio De Santis wrote:
> why??

What ruby are you using? With ruby 1.8.7 (2010-01-10 patchlevel 249)
[x86_64-linux] and your posted code, I get the following output:

["a", "ab"]
"b"
ert.rb:17:in `[]': can't convert Regexp into Integer (TypeError)
from ert.rb:17

If I change it to

alias_method :slice_without_regexp, :slice
alias_method :slice, :slice_with_regexp
alias_method :[], :slice_with_regexp

then *that* gives a stack too deep error, but on the initial slice call.

I'm afraid I don't know the solution though. I suspect slice is already
an alias for [], or vice versa.
--
Posted via http://www.ruby-forum.com/.

From: David A. Black on 1 Aug 2010 07:57
Hi --

On Sun, 1 Aug 2010, Brian Candler wrote:

> Maurizio De Santis wrote:
>> why??
>
> What ruby are you using? With ruby 1.8.7 (2010-01-10 patchlevel 249)
> [x86_64-linux] and your posted code, I get the following output:
>
> ["a", "ab"]
> "b"
> ert.rb:17:in `[]': can't convert Regexp into Integer (TypeError)
> from ert.rb:17
>
> If I change it to
>
> alias_method :slice_without_regexp, :slice
> alias_method :slice, :slice_with_regexp
> alias_method :[], :slice_with_regexp
>
> then *that* gives a stack too deep error, but on the initial slice call.
>
> I'm afraid I don't know the solution though. I suspect slice is already
> an alias for [], or vice versa.

They are indeed the same method:

rb_define_method(rb_cArray, "[]", rb_ary_aref, -1);
rb_define_method(rb_cArray, "slice", rb_ary_aref, -1);


David

--
David A. Black, Senior Developer, Cyrus Innovation Inc.

The Ruby training with Black/Brown/McAnally
Compleat Philadelphia, PA, October 1-2, 2010
Rubyist http://www.compleatrubyist.com

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