Asp Forum - Object methods

Eustaquio Rangel de Oliveira Jr.

3/25/2006 2:23:00 PM

Hello there. :-)

Ok, I know I can do this to add a method (and a class)
to an object:

irb(main):001:0> s = "Testing!"
=> "Testing!"
irb(main):002:0> class <<s
irb(main):003:1> def says
irb(main):004:2> puts "s says:"+self
irb(main):005:2> end
irb(main):006:1> end
=> nil
irb(main):007:0> s.says
s says:Testing!
=> nil
irb(main):008:0> x = "Another test."
=> "Another test."
irb(main):009:0> x.says
NoMethodError: undefined method `says' for "Another
test.":String
from (irb):9
from :0
irb(main):010:0>

My question is, dinamically, how to do that? Just like
this:

irb(main):010:0> x.class.class_eval %q(def x.says()
puts "x says:"+self end)
=> nil
irb(main):011:0> x.says
x says:Another test.

Or there is another shorter way to do that, with an
object? To build an object method with some parameters
like a string or a Proc?

Thanks! :-)

----------------------------
Eustáquio "TaQ" Rangel
eustaquiorangel@yahoo.com
http://b...
Usuário GNU/Linux no. 224050

13 Answers

Robert Klemme

3/25/2006 10:50:00 PM

Eustaquio Rangel de Oliveira J wrote:
> Hello there. :-)
>
> Ok, I know I can do this to add a method (and a class)
> to an object:
>
> irb(main):001:0> s = "Testing!"
> => "Testing!"
> irb(main):002:0> class <<s
> irb(main):003:1> def says
> irb(main):004:2> puts "s says:"+self
> irb(main):005:2> end
> irb(main):006:1> end
> => nil
> irb(main):007:0> s.says
> s says:Testing!
> => nil
> irb(main):008:0> x = "Another test."
> => "Another test."
> irb(main):009:0> x.says
> NoMethodError: undefined method `says' for "Another
> test.":String
> from (irb):9
> from :0
> irb(main):010:0>
>
> My question is, dinamically, how to do that? Just like
> this:
>
> irb(main):010:0> x.class.class_eval %q(def x.says()
> puts "x says:"+self end)
> => nil
> irb(main):011:0> x.says
> x says:Another test.
>
> Or there is another shorter way to do that, with an
> object? To build an object method with some parameters
> like a string or a Proc?

I'm not sure what exactly you're after. Do you mean

class String
def says
print "s says: ", self, "\n"
end
end

?

robert

Eustaquio Rangel de Oliveira Jr.

3/25/2006 11:08:00 PM

Hello, Robert!

> I'm not sure what exactly you're after. Do you mean
> class String
> def says
> print "s says: ", self, "\n"
> end
> end
> ?

Not really, I want to create a new method on the
object, after it's created, but not on the class. As
the previous example of

s = "Testing"
class <<s
def says
print "s says: ", self, "\n"
end
end

where it creates the method (and all that metaclass
stuff).

At this point just, just s have the "says" method, not
the class String or any other String object that was
created or will be created. Using

s.class.class_eval %q(def x.says() puts "x says:"+self
end)

have the same effect, but what I like to know if there
is another way to do that. I mean, create a method on
a specific object (on this case, just "s"), not on the
class.

Best regards,

----------------------------
Eustáquio "TaQ" Rangel
eustaquiorangel@yahoo.com
http://b...
Usuário GNU/Linux no. 224050

Eustaquio Rangel de Oliveira Jr.

3/25/2006 11:17:00 PM

Oooooops, sorry for this. The correct example is:

s.class.class_eval %q(def s.says() puts "s says:"+self
end)

I copied the wrong part of my previous email. :-p

Best regards,

----------------------------
Eustáquio "TaQ" Rangel
eustaquiorangel@yahoo.com
http://b...
Usuário GNU/Linux no. 224050

Tim Hunter

3/25/2006 11:18:00 PM

Eustaquio Rangel de Oliveira J wrote:
> Hello, Robert!
>
>
>>I'm not sure what exactly you're after. Do you mean
>>class String
>> def says
>> print "s says: ", self, "\n"
>> end
>>end
>>?
>
>
> Not really, I want to create a new method on the
> object, after it's created, but not on the class. As
> the previous example of
>
> s = "Testing"
> class <<s
> def says
> print "s says: ", self, "\n"
> end
> end
>
> where it creates the method (and all that metaclass
> stuff).
>
> At this point just, just s have the "says" method, not
> the class String or any other String object that was
> created or will be created. Using
>
> s.class.class_eval %q(def x.says() puts "x says:"+self
> end)
>
> have the same effect, but what I like to know if there
> is another way to do that. I mean, create a method on
> a specific object (on this case, just "s"), not on the
> class.
>
> Best regards,
>
> ----------------------------
> Eustáquio "TaQ" Rangel
> eustaquiorangel@yahoo.com
> http://b...
> Usuário GNU/Linux no. 224050
>
>

Hmmm...you can use Object#extend to add the instance methods from a
module. Is that what you're looking for?

dblack

3/26/2006 1:42:00 AM

Robert Klemme

3/26/2006 10:50:00 AM

Eustaquio Rangel de Oliveira J wrote:
> Hello, Robert!
>
>> I'm not sure what exactly you're after. Do you mean
>> class String
>> def says
>> print "s says: ", self, "\n"
>> end
>> end
>> ?
>
> Not really, I want to create a new method on the
> object, after it's created, but not on the class. As
> the previous example of
>
> s = "Testing"
> class <<s
> def says
> print "s says: ", self, "\n"
> end
> end
>
> where it creates the method (and all that metaclass
> stuff).
>
> At this point just, just s have the "says" method, not
> the class String or any other String object that was
> created or will be created. Using
>
> s.class.class_eval %q(def x.says() puts "x says:"+self
> end)
>
> have the same effect,

This doesn't work for me. You define a method "say" for an instance "x"
in the scope of the class. You probably want something else.

> but what I like to know if there
> is another way to do that. I mean, create a method on
> a specific object (on this case, just "s"), not on the
> class.

def s.says
puts "I say " + self
end

It would certainly help if you tell us what problem you are trying to solve.

Cheers

robert

Eustaquio Rangel de Oliveira Jr.

3/26/2006 2:15:00 PM

Hi, David.

> How about:
>
> def s.says
> puts "s says: #{self}"
> end
> ?

Yes, this way works, but I need to make it
dinamically, for example (don't know if it's a valid
situation, just curious about) reading the code from a
string from a file. If I type the code above it's ok,
but I want to load the new methods from somewhere.

Best regards,

----------------------------
Eustáquio "TaQ" Rangel
eustaquiorangel@yahoo.com
http://b...
Usuário GNU/Linux no. 224050

Eustaquio Rangel de Oliveira Jr.

3/26/2006 2:17:00 PM

Hi, Tim!

> Hmmm...you can use Object#extend to add the instance
> methods from a
> module. Is that what you're looking for?

But on that way I need a previou module with the
methods. What I want is to create the methods on a
certain object, "on the air", I mean, from a string or
something like that.

The s.class.class_eval <string here> make this kind of
thing, but I was curious about some other way to do
that. :-)

Best regards,

----------------------------
Eustáquio "TaQ" Rangel
eustaquiorangel@yahoo.com
http://b...
Usuário GNU/Linux no. 224050

Eustaquio Rangel de Oliveira Jr.

3/26/2006 2:45:00 PM

Hi Robert!

> > s.class.class_eval %q(def x.says() puts "x
> says:"+self
> > end)
> This doesn't work for me. You define a method "say"
> for an instance "x"
> in the scope of the class. You probably want
> something else.

I noticed that I made a mistake there and correct it
on another email few seconds after that one. Sorry
about that. My fault.

As I told on the other email, the correct thing is

s.class.class_eval %q(def s.says() puts "s says:"+self
end)

So I create a method "says" only on the object s (not
on the class String where it belongs to).

> It would certainly help if you tell us what problem
> you are trying to solve.

Ok, not really a problem, I was just curious about it.

Let's imagine that I need a way to create methods on
*specific objects*, not on their classes. The methods
are stored on some file or the user type it when using
the program (ok, I know the security concerns about
that :-), and I find them later using some reflection
and respond_to calls.

So at some point the user knows (again, don't know if
its a valid situation) that there are some String
objects hangin' there, s and x, and says "hey, add
this method I defined here on this text field, as a
string, to the s object, but *just to it*, not to its
class or other String objects". On this case, knowing
that I want to create the method just on s, and it's a
String, I can use

String.class_eval %q(def s.says() puts "s says:"+self
end)

to make this works, and ask for some reavaliation of
the current objects, where it will tell me that the s
object, yes, have a "says" method there.

s.respond_to?(:says)

It works this way, I was just curious if there is not
an *object method* to do that, not using the class to
make it works. But works this way because of the need
to add a virtual class to s to hold the says() method,
right?

Best regards,

----------------------------
Eustáquio "TaQ" Rangel
eustaquiorangel@yahoo.com
http://b...
Usuário GNU/Linux no. 224050

Patrick Hof

3/26/2006 3:49:00 PM

Eustaquio Rangel de Oliveira J <eustaquiorangel@yahoo.com> schrieb:

> Let's imagine that I need a way to create methods on
> *specific objects*, not on their classes. The methods
> are stored on some file or the user type it when using
> the program (ok, I know the security concerns about
> that :-), and I find them later using some reflection
> and respond_to calls.

Erm, maybe you're searching for "instance_eval"?

Patrick

--
'Today Is A Good Day For Someone Else To Die!'
(Feet of Clay)

comp.lang.ruby

Object methods

Eustaquio Rangel de Oliveira Jr.

Robert Klemme

Eustaquio Rangel de Oliveira Jr.

Eustaquio Rangel de Oliveira Jr.

Tim Hunter

dblack

Robert Klemme

Eustaquio Rangel de Oliveira Jr.

Eustaquio Rangel de Oliveira Jr.

Eustaquio Rangel de Oliveira Jr.

Patrick Hof

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