Execute block in context of yielding method's module

ruby-talk
#1

Mental block. Is there a reasonable way to do this?

  def dothis ; puts "NO!" ; end

  module M
    class << self
      def dothis
        puts "THIS" + @number.to_s
      end
      def wrap( n, &yld )
        old = @number
        @number = n
        yld.call
        @number = old
      end
    end
  end

  M.wrap( 10 ) do
    dothis
  end

This produces "NO!". How do I get it to execute the block in the
context of M, so that it produces "THIS10" (w/o having to out
M.dothis).

Thanks,
T.

#2

instance_eval is the standard way of changing 'self':

   M.instance_eval { wrap(10) { dothis } }

David

···

On Sat, 12 Nov 2005, Trans wrote:

Mental block. Is there a reasonable way to do this?

def dothis ; puts "NO!" ; end

module M
   class << self
     def dothis
       puts "THIS" + @number.to_s
     end
     def wrap( n, &yld )
       old = @number
       @number = n
       yld.call
       @number = old
     end
   end
end

M.wrap( 10 ) do
   dothis
end

This produces "NO!". How do I get it to execute the block in the
context of M, so that it produces "THIS10" (w/o having to out
M.dothis).

--
David A. Black
dblack@wobblini.net

#3

Use
  instance_eval &yld
instead of
  yld.call
?

Regards,

Sean

#4

Ah, right. Thanks.

T.

#5

Hey guys,

I'm very new to ruby.

This is some freaky shite! Could somebody give me a use case as to when I'd
want to do something like this?

Thanks!

···

On 11/12/05, Trans <transfire@gmail.com> wrote:

Ah, right. Thanks.

T.

--
-

Christian Leskowsky
christian.leskowsky@gmail.com

#6

harp:~ > cat a.rb
   module Connection
     class << self
       def host arg = nil
         @host = arg if arg
         @host
       end
       def port arg = nil
         @port = arg if arg
         @port
       end
       def configure &block
         instance_eval &block
       end
     end
   end

   Connection::configure do
     host 'http://codeforpeople.com'
     port 80
   end

   p Connection::host
   p Connection::port

   harp:~ > ruby a.rb
   "http://codeforpeople.com"
   80

regards.

-a

···

On Sun, 13 Nov 2005, Christian Leskowsky wrote:

Hey guys,

I'm very new to ruby.

This is some freaky shite! Could somebody give me a use case as to when I'd
want to do something like this?

Thanks!

--

ara [dot] t [dot] howard [at] gmail [dot] com
all happiness comes from the desire for others to be happy. all misery
comes from the desire for oneself to be happy.
-- bodhicaryavatara

===============================================================================

#7

Hi --

Hey guys,

I'm very new to ruby.

This is some freaky shite! Could somebody give me a use case as to when I'd
want to do something like this?

Somewhat rarely :slight_smile: I actually prefer to know what 'self' is when I
write a block. I'm uneasy with the idea that here:

   some_method { another_method }

I can't tell by looking who's receiving the another_method message.

A more common idiom is to provide the object so that you can see
exactly who's doing what:

   class C
     attr_accessor :x
     def initialize
       yield self
     end
   end

   C.new do |c|
     c.x = 1
   end

and things like that.

David

···

On Sun, 13 Nov 2005, Christian Leskowsky wrote:

--
David A. Black
dblack@wobblini.net

#8

Interesting... Thanks!

···

On 11/12/05, Ara.T.Howard <ara.t.howard@noaa.gov> wrote:

On Sun, 13 Nov 2005, Christian Leskowsky wrote:

> Hey guys,
>
> I'm very new to ruby.
>
> This is some freaky shite! Could somebody give me a use case as to when
I'd
> want to do something like this?
>
> Thanks!

harp:~ > cat a.rb
module Connection
class << self
def host arg = nil
@host = arg if arg
@host
end
def port arg = nil
@port = arg if arg
@port
end
def configure &block
instance_eval &block
end
end
end

Connection::configure do
host 'http://codeforpeople.com'
port 80
end

p Connection::host
p Connection::port

harp:~ > ruby a.rb
"http://codeforpeople.com"
80

regards.

-a
--

===============================================================================
> ara [dot] t [dot] howard [at] gmail [dot] com
> all happiness comes from the desire for others to be happy. all misery
> comes from the desire for oneself to be happy.
> -- bodhicaryavatara

===============================================================================

--
-

'There was an owl lived in an oak.
The more he heard, the less he spoke.
The less he spoke, the more he heard.'

Christian Leskowsky
christian.leskowsky@gmail.com

#9

Thanks for the reply guys!

This last one looks much better to my eyes, but I'm still having problems.

I like the code I write to tell as much to the reader about what's going on
as it possibly can-right there (without having to jump to other methods, in
other classes, in other modules).

I think I'd probably have a hard time figuring out what:

C.new do |c|
c.x = 1
end

did, without having:

class C
attr_accessor :x
def initialize
yield self
end
end

being directly above it (on the same screen somewhere). It might take a few
more keystrokes to write:

c = C.new
c.x = 1

in general, but to me, it's much more readable.

The other thing that bugs me (and it's probably just an unfortunate
example), is that it looks like I'm passing out a reference to myself,
before I'm completely initialized. ugh!

Strange stuff... I think I'll just stay about as for away from it as I can
:).

···

--
-

'There was an owl lived in an oak.
The more he heard, the less he spoke.
The less he spoke, the more he heard.'

Christian Leskowsky
christian.leskowsky@gmail.com

On 11/13/05, David A. Black <dblack@wobblini.net> wrote:

Hi --

On Sun, 13 Nov 2005, Christian Leskowsky wrote:

> Hey guys,
>
> I'm very new to ruby.
>
> This is some freaky shite! Could somebody give me a use case as to when
I'd
> want to do something like this?

Somewhat rarely :slight_smile: I actually prefer to know what 'self' is when I
write a block. I'm uneasy with the idea that here:

some_method { another_method }

I can't tell by looking who's receiving the another_method message.

A more common idiom is to provide the object so that you can see
exactly who's doing what:

class C
attr_accessor :x
def initialize
yield self
end
end

C.new do |c|
c.x = 1
end

and things like that.

David

--
David A. Black
dblack@wobblini.net

#10

Hi --

Thanks for the reply guys!

This last one looks much better to my eyes, but I'm still having problems.

I like the code I write to tell as much to the reader about what's going on
as it possibly can-right there (without having to jump to other methods, in
other classes, in other modules).

I think I'd probably have a hard time figuring out what:

C.new do |c|
c.x = 1
end

did, without having:

class C
attr_accessor :x
def initialize
yield self
end

being directly above it (on the same screen somewhere). It might take a few
more keystrokes to write:

c = C.new
c.x = 1

in general, but to me, it's much more readable.

Actually I just showed the construct without assignment. In full
you'd want to assign it:

   mc = MyClass.new do |m|
     m.x = 1
   end

(Easier to choose names with a multi-letter class name :slight_smile:

Or if c existed already:

   c = nil
   C.new do |c| etc.

because the block params pick up any existing variables and use those.
(This may change circa 2.0.)

Also, most of the time you see this, there's more than one assignment
going on in the block, so it has a nice encapsulating feel.

Mind you, all of this would have to go hand-in-hand with
documentation. You probably wouldn't have the method code visible,
but you'd have to know that MyClass.new yielded the new instance.

David

···

On Mon, 14 Nov 2005, Christian Leskowsky wrote:

The other thing that bugs me (and it's probably just an unfortunate
example), is that it looks like I'm passing out a reference to myself,
before I'm completely initialized. ugh!

Strange stuff... I think I'll just stay about as for away from it as I can
:).

--
-

'There was an owl lived in an oak.
The more he heard, the less he spoke.
The less he spoke, the more he heard.'

Christian Leskowsky
christian.leskowsky@gmail.com

On 11/13/05, David A. Black <dblack@wobblini.net> wrote:

Hi --

On Sun, 13 Nov 2005, Christian Leskowsky wrote:

Hey guys,

I'm very new to ruby.

This is some freaky shite! Could somebody give me a use case as to when

I'd

want to do something like this?

Somewhat rarely :slight_smile: I actually prefer to know what 'self' is when I
write a block. I'm uneasy with the idea that here:

some_method { another_method }

I can't tell by looking who's receiving the another_method message.

A more common idiom is to provide the object so that you can see
exactly who's doing what:

class C
attr_accessor :x
def initialize
yield self
end

C.new do |c|
c.x = 1
end

and things like that.

David

--
David A. Black
dblack@wobblini.net

--
David A. Black
dblack@wobblini.net