Understanding aRegexp === aString

ruby-talk
1

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 ???

···

--
une bévue

2

i'm experiencing with regexp and ruby and follo the page
<http://www.rubycentral.com/book/ref_c_regexp.html&gt;

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 ???

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)

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 ???

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).

···

On Thu, 2006-03-23 at 23:13 +0900, Une bévue wrote:

--
Ross Bamford - rosco@roscopeco.REMOVE.co.uk

3

(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 :wink:

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

ok, thanks very much !

···

Ross Bamford <rossrt@roscopeco.co.uk> wrote:
--
une bévue

4

Ross Bamford 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

···

On Thu, 2006-03-23 at 23:13 +0900, Une bévue wrote:

5

Robert Klemme wrote:

Ross Bamford 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

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

···

On Thu, 2006-03-23 at 23:13 +0900, Une bévue wrote:

--
      vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

6

Robert Klemme wrote:

Ross Bamford 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

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

···

On Thu, 2006-03-23 at 23:13 +0900, Une bévue wrote:

--
      vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

7

In Message-Id: <48fqlkFjiogvU1@individual.net>
Robert Klemme <bob.news@gmx.net> 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"

···

--
kjana@dm4lab.to March 24, 2006
Whatever is worth doing at all is worth doing well.

8

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?

···

--
- Stephen Bannasch
   Concord Consortium, http://www.concord.org

9

Use the tag! method...

x.security {
  x.tag! "all-permissions" {

  }
}

Hope this helps.

Josh

···

On 3/23/06, Stephen Bannasch <stephen.bannasch@gmail.com> wrote:

...

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?

10

YANAGAWA Kazuhisa wrote:

In Message-Id: <48fqlkFjiogvU1@individual.net>
Robert Klemme <bob.news@gmx.net> 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"

Good point! Thanks to you and Joel!

Kind regards

  robert

11

Thanks Josh. That did indeed help! It is much simpler than the way I was trying to solve the problem.

···

Use the tag! method...

x.security {
x.tag! "all-permissions" {

}
}

--
- Stephen Bannasch
  Concord Consortium, http://www.concord.org