Forum: Ruby understanding aRegexp === aString

Announcement (2017-05-07): www.ruby-forum.com is now read-only since I unfortunately do not have the time to support and maintain the forum any more. Please see rubyonrails.org/community and ruby-lang.org/en/community for other Rails- und Ruby-related community platforms.
unknown (Guest)
on 2006-03-23 16:13
(Received via mailing list)
i'm experiencing with regexp and ruby and follo the page
<http://www.rubycentral.com/book/ref_c_regexp.html>

at "===" i've found an example :

a = "HELLO"
case a
when /^a-z*$/; print "Lower case\n"
when /^A-Z*$/; print "Upper case\n"
else;            print "Mixed case\n"
end

saying it produces :
# => Upper case

i got :

Mixed case

why this discrapency, if any ???

is that due to the fact my script file is UTF-8 encoded ???

also with :
truc = 'toto'
rgx=Regexp.new('^toto$')
flag=(truc =~ rgx)? true : false
p "flag = #{flag}"
# => "flag = true"
flag=(truc === rgx) /// this one i don't understand the result
p "flag = #{flag}"
# => "flag = false"
flag=(truc == rgx)
p "flag = #{flag}"
# => "flag = false"
flag=(truc =~ rgx)
p "flag = #{flag}"
# => "flag = 0"

why, when aString = 'toto' and ARegexp = Regexp.new('^toto$')

the equality "===" returns false ???
Ross B. (Guest)
on 2006-03-23 16:37
(Received via mailing list)
On Thu, 2006-03-23 at 23:13 +0900, Une bévue wrote:
> end
>
> saying it produces :
> # => Upper case
>
> i got :
>
> Mixed case
>
> why this discrapency, if any ???
>

I guess that's a typo on the site, it's correct in my printed 2nd ed:

a = "HELLO"
case a
when /^[a-z]*$/; print "Lower case\n"
when /^[A-Z]*$/; print "Upper case\n"
else;            print "Mixed case\n"
end

# -> Upper Case

(Notice the [] brackets that denote a character set)

> p "flag = #{flag}"
> # => "flag = false"
> flag=(truc =~ rgx)
> p "flag = #{flag}"
> # => "flag = 0"
>
> why, when aString = 'toto' and ARegexp = Regexp.new('^toto$')
>
> the equality "===" returns false ???
>

Try this:

truc = 'toto'
rgx=Regexp.new('^toto$')
flag=(truc =~ rgx)? true : false
p "flag = #{flag}"
# => "flag = true"
flag=(rgx === truc) # /// switch these around
p "flag = #{flag}"
# => "flag = true"
flag=(truc == rgx)
p "flag = #{flag}"
# # => "flag = false"
flag=(truc =~ rgx)
p "flag = #{flag}"
# # => "flag = 0"

See also the 'what on earth...' thread that's been on the list recently
(yesterday/today I think).
Robert K. (Guest)
on 2006-03-23 16:48
(Received via mailing list)
Ross B. wrote:
> On Thu, 2006-03-23 at 23:13 +0900, Une bévue wrote:

>> the equality "===" returns false ???

Adding to Ross' excellent explanation: it helps to *not* view "===" as
an equality operator.  Rather it's a general matching operator, whatever
matching means in a certain context.  For RX it will do an RX match, for
class objects it will do the kind_of? check, for a range it will check
include? etc.  Btw, has anyone an idea why this does not apply to
Enumerable?

 >> [1,2,3].include? 2
=> true
 >> [1,2,3] === 2
=> false

Kind regards

	robert
unknown (Guest)
on 2006-03-23 16:49
(Received via mailing list)
Ross B. <removed_email_address@domain.invalid> wrote:

> (Notice the [] brackets that denote a character set)

fine, thanks, difficult to catch out typos particularly in regexps...

>
>
> Try this:
>
[...]

> flag=(rgx === truc) # /// switch these around
> p "flag = #{flag}"
> # => "flag = true"

i did both :
flag=(truc === rgx)
p "flag = #{flag} for flag=(truc === rgx)"
# => "flag = false for flag=(truc === rgx)""
flag=(rgx === truc)
p "flag = #{flag} for flag=(rgx === truc)"
# => "flag = true for flag=(rgx === truc)"

that's a really strange behaviour, to me, of ruby, a "symetrical"
operator symbol being not commutative ????

better to know ;-)

>
> See also the 'what on earth...' thread that's been on the list recently
> (yesterday/today I think).

ok, thanks very much !
Joel VanderWerf (Guest)
on 2006-03-23 19:28
(Received via mailing list)
Robert K. wrote:
> Enumerable?
>
>>> [1,2,3].include? 2
> => true
>>> [1,2,3] === 2
> => false

It would be nice, but then how would this work:

irb(main):001:0> case [1,2,3]
irb(main):002:1> when [1,2,3]
irb(main):003:1>   puts "same array!"
irb(main):004:1> end
same array!
=> nil
Joel VanderWerf (Guest)
on 2006-03-23 19:42
(Received via mailing list)
Robert K. wrote:
> Enumerable?
>
>>> [1,2,3].include? 2
> => true
>>> [1,2,3] === 2
> => false

It would be nice, but then how would this work:

irb(main):001:0> case [1,2,3]
irb(main):002:1> when [1,2,3]
irb(main):003:1>   puts "same array!"
irb(main):004:1> end
same array!
=> nil
Stephen B. (Guest)
on 2006-03-24 00:05
(Received via mailing list)
I'm trying to use builder to construct jnlp files. I need to create
elements with "-" in the name and can't. For example I need to output
the following xml fragment:

<security>
   <all-permissions />
</security>

Here's what I tried with builder:

x = Builder::XmlMarkup.new(:target => $stdout, :indent => 1)

x.security {
  x.all-permissions
}

but the "-" is parsed in the name and this produces a NameError

   NameError: undefined local variable or method `permissions' for
main:Object

Is there a way to do this?
YANAGAWA Kazuhisa (Guest)
on 2006-03-24 01:18
(Received via mailing list)
In Message-Id: <removed_email_address@domain.invalid>
Robert K. <removed_email_address@domain.invalid> writes:

>  >> [1,2,3].include? 2
> => true
>  >> [1,2,3] === 2
> => false

Once that can be but "fixed" later since.... it can be a seed of
confusion and we can use "*" for array on when clause.

  n = 2
  array = [2, 4, 6]

  case n
  when *array
    puts "foo"
  else
    puts "bar"
  end

  # prints "foo"
Robert K. (Guest)
on 2006-03-24 11:38
(Received via mailing list)
YANAGAWA Kazuhisa wrote:
>
>   # prints "foo"
Good point!  Thanks to you and Joel!

Kind regards

	robert
This topic is locked and can not be replied to.