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comp.lang.ruby

redefine Kernel method

koboi

2/9/2005 8:29:00 PM

I would like to redefine the method Kernel#rand inside a test method, and
reset it in the end again.
But everything I try fails. If I redefine it outside my module and class,
it works. But I would like to do it inside my test method.

Thx for any hint.
Daniel
5 Answers

Zach Dennis

2/9/2005 10:02:00 PM

0

koboi wrote:
> I would like to redefine the method Kernel#rand inside a test method, and
> reset it in the end again.
> But everything I try fails. If I redefine it outside my module and class,
> it works. But I would like to do it inside my test method.
>

def meth
m = proc { 5 }
Kernel.module_eval( "alias :rand_old :rand" )
Kernel.module_eval( "def rand; #{m.call}; end" )
puts rand
Kernel.module_eval( "alias :rand :rand_old" )
Kernel.module_eval( "remove_method( :rand_old ) " )
end

meth
puts rand

I hope this moves you in the right direction,

Zach

koboi

2/10/2005 10:44:00 PM

0

It moves in the right direction, yes, thanks.
But still, it doesn't work as I would like. If I want to count, how many
times the method is called, the Proc is evaluated only once, so the count
is always 1.
Example:
@count = 0
m = proc { @count += 1; 5 }
#...
#call rand several times
p @count -> 1

Any suggestions.
thanks, daniel

Zach Dennis

2/10/2005 11:02:00 PM

0

koboi wrote:
> It moves in the right direction, yes, thanks.
> But still, it doesn't work as I would like. If I want to count, how many
> times the method is called, the Proc is evaluated only once, so the count
> is always 1.
> Example:
> @count = 0
> m = proc { @count += 1; 5 }
> #...
> #call rand several times
> p @count -> 1
>

I'm going to repost after i figure this one out, the problem with my
first post (and i apologize for posting inaccurate code), was that the
"#{m.call}" was getting evaluated in the 'module_eval( "..." )' and it
wasn't actually getting called when rand got called.

Kernel.module_eval( "def rand; #{m.call}; end" )

Will have rand return the value of m.call. It will always return the
same thing, because m.call is evaluated in the String, and not when rand
is called.

m = proc { 50 }
def rand; #{m.call}; end

is the same as:

def rand; 50; end

working on a solution,

Zach

Zach Dennis

2/10/2005 11:08:00 PM

0

Ok, here's what you want Daniel;

def meth
str =<<-"ENDSTR"
alias :rand_old :rand
@@rand_call_count = 0
def rand
@@rand_call_count += 1
puts @@rand_call_count
rand_old
end
ENDSTR
Kernel.module_eval( str )
rand
rand
rand
rand
Kernel.module_eval( "alias :rand :rand_old" )
Kernel.module_eval( "remove_method( :rand_old ) " )
end

meth

This will still allow rand to return the correct value, and it will get
count for you.

This is a cleaner solution then before.

HTH,

Zach

koboi

2/12/2005 12:32:00 PM

0

Just used your new version, it works now. Thanks a lot for your help.

There is only one little change:
....
def rand(max = 0)
....

Thx,
Daniel