# How can I monitor a Regexp?

**URL:** <https://www.ruby-forum.com/t/how-can-i-monitor-a-regexp/87102>\
**Category:** Ruby\
**Created:** [February 28, 2007, 6:55am UTC](https://www.ruby-forum.com/t/how-can-i-monitor-a-regexp/87102 "2007-02-28T06:55:29Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![Daniel\_DeLorme](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9d8465/32.png) [@Daniel\_DeLorme](https://www.ruby-forum.com/u/Daniel_DeLorme)\
**Post date:** [February 28, 2007, 6:55am UTC](https://www.ruby-forum.com/t/how-can-i-monitor-a-regexp/87102/1 "2007-02-28T06:55:29Z")

</div>

Because a regular expression can have different behaviors depending on  
its kcode  
(e.g. behavior of \w) I decided that all my code should specify the  
kcode  
explicitly (e.g. /\w+/n instead /\w+/). So I tried to set up some hooks  
to  
monitor the creation of each Regexp and raise an exception if the kcode  
is  
missing. Like this:

class Regexp  
alias old\_initialize initialize  
def initialize(\*args)  
old\_initialize(\*args)  
raise “NO KCODE!” if kcode.nil?  
end  
end

And it works fine if I use Regexp.new, but in the majority of cases the  
regexp  
is expressed as a literal and the initialize is NOT EXECUTED.

> Regexp.new(“foobar”)  
> RuntimeError: NO KCODE!  
> /foobar/  
> =\> /foobar/

So I tried an alternate approach and set the hook into the =~ operator,  
but same  
problem; the method override is completely ignored:  
class String; def =~(o); raise “S”; end; end  
class Regexp; def =~(o); raise “R”; end; end  
“bar” =~ /bar/ #=\> 0  
/foo/ =~ “foo” #=\> 0

So… anyone has any idea how I can tackle that problem?

---

<div class="post-metadata">

**Author:** ![Daniel\_DeLorme](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9d8465/32.png) [@Daniel\_DeLorme](https://www.ruby-forum.com/u/Daniel_DeLorme)\
**Post date:** [February 28, 2007, 11:36am UTC](https://www.ruby-forum.com/t/how-can-i-monitor-a-regexp/87102/2 "2007-02-28T11:36:51Z")

</div>

ruby -v

# ==\> ruby 1.8.4 (2005-12-24) [i486-linux]

class String; def =~(o); raise “S”; end; end  
class Regexp; def =~(o); raise “R”; end; end

r = /x/  
r =~ ‘a’

# ==\> RuntimeError: R

```
    from (irb):2:in `=~'
    from (irb):4

```

‘a’ =~ r

# ==\> RuntimeError: S

```
    from (irb):1:in `=~'
    from (irb):5
```

---

<div class="post-metadata">

**Author:** ![Daniel\_DeLorme](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9d8465/32.png) [@Daniel\_DeLorme](https://www.ruby-forum.com/u/Daniel_DeLorme)\
**Post date:** [February 28, 2007, 11:25am UTC](https://www.ruby-forum.com/t/how-can-i-monitor-a-regexp/87102/3 "2007-02-28T11:25:52Z")

</div>

On 2/28/07, Daniel DeLorme [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> ```
> raise "NO KCODE!" if kcode.nil?
> 
> ```
> 
> So I tried an alternate approach and set the hook into the =~ operator, but same  
> problem; the method override is completely ignored:  
> class String; def =~(o); raise “S”; end; end  
> class Regexp; def =~(o); raise “R”; end; end  
> “bar” =~ /bar/ #=\> 0  
> /foo/ =~ “foo” #=\> 0
> 
> So… anyone has any idea how I can tackle that problem?

Yes, well no, I had one, but prospects look bleak now, look at this

robert@swserver:/home/svn 11:49:44  
555/56 \> ruby -r profile -e ‘puts /a/’  
(?-mix:a)  
% cumulative self self total  
time seconds seconds calls ms/call ms/call name  
0.00 0.00 0.00 2 0.00 0.00 IO#write  
0.00 0.00 0.00 1 0.00 0.00 Regexp#to\_s  
0.00 0.00 0.00 1 0.00 0.00 Kernel.puts  
0.00 0.01 0.00 1 0.00 10.00 #toplevel  
robert@swserver:/home/svn 11:49:50  
556/57 \> ruby -r profile -e ‘puts Regexp.new(“a”)’  
(?-mix:a)  
% cumulative self self total  
time seconds seconds calls ms/call ms/call name  
0.00 0.00 0.00 2 0.00 0.00 IO#write  
0.00 0.00 0.00 1 0.00 0.00 Kernel.puts  
0.00 0.00 0.00 1 0.00 0.00 Regexp#initialize  
0.00 0.00 0.00 1 0.00 0.00 Class#new  
0.00 0.00 0.00 1 0.00 0.00 Regexp#to\_s  
0.00 0.01 0.00 1 0.00 10.00 #toplevel

I just do not see any way to intercept on Ruby level, you would need  
to hack ruby itself.  
Maybe someone more clever than me?

Cheers  
Robert

---

<div class="post-metadata">

**Author:** ![Daniel\_DeLorme](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9d8465/32.png) [@Daniel\_DeLorme](https://www.ruby-forum.com/u/Daniel_DeLorme)\
**Post date:** [February 28, 2007, 12:58pm UTC](https://www.ruby-forum.com/t/how-can-i-monitor-a-regexp/87102/4 "2007-02-28T12:58:02Z")

</div>

Jan F. wrote:

> ```
> from (irb):4
> 
> ```
> 
> ‘a’ =~ r
> 
> # ==\> RuntimeError: S
> 
> ```
> from (irb):1:in `=~'
> from (irb):5
> 
> ```

Very interesting. If you assign the regexp to a variable you get  
the overridden methods. I guess there’s some voodoo optimization  
at work when you use =~ on a regexp literal?

Daniel

---

<div class="post-metadata">

**Author:** ![Daniel\_DeLorme](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9d8465/32.png) [@Daniel\_DeLorme](https://www.ruby-forum.com/u/Daniel_DeLorme)\
**Post date:** [February 28, 2007, 2:17pm UTC](https://www.ruby-forum.com/t/how-can-i-monitor-a-regexp/87102/5 "2007-02-28T14:17:22Z")

</div>

Daniel DeLorme wrote:

> Because a regular expression can have different behaviors depending on  
> its kcode (e.g. behavior of \w) I decided that all my code should  
> specify the kcode explicitly (e.g. /\w+/n instead /\w+/).

As an addendum, I was wondering why \w matches extended characters in  
utf8.  
If extended characters are considered “word” characters, does it mean  
they  
are valid for identifiers? So I tried:

> $KCODE=‘u’  
> =\> “u”  
> def 日本語  
> “nihongo”  
> end  
> =\> nil  
> 日本語  
> =\> “nihongo”

wow. O\_O

Daniel