Scope of block

ruby-talk
1

Hello i have a question about scopes of block
I want to define a block at one time.
But when it get's called it should have the scope (vars ed )
of the calling environement

Example :

···

------------------------------

class BlockTest

  attr_accessor :myblock

  def process(&block)
    self.myblock = block
  end
end

t = BlockTest.new
t.process {

  "var = #{out_of_scope_var}"
  }

out_of_scope_var = "daniel"
p t.myblock.call

Results in :

blocktest.rb:15: undefined local variable or method `out_of_scope_var'
for main:Object (NameError) from blocktest.rb:19

How can i call the proc so that the out_of_scope_var is known :

result would be :

so i would get :

daniel-wijnands-powerbook58-2:~/jim/vendor/plugins/widget_grid/lib
danielwijnands$ ruby blocktest.rb
"var = daniel"

2

daniel wrote:

Hello i have a question about scopes of block
I want to define a block at one time.
But when it get's called it should have the scope (vars ed )
of the calling environement

Perhaps you will be satisfied that the block receive values from the parent
environment. This is the normal way to solve the problem.

···

--------------------------------

#!/usr/bin/ruby -w

class BlockTest

   attr_accessor :myblock
   def process(&block)
      self.myblock = block
   end
end

t = BlockTest.new
t.process{ |v|
   "var = #{v}"
}

v = "daniel"
p t.myblock.call(v)

--------------------------------

"var = daniel"

--
Paul Lutus
http://www.arachnoid.com

3

daniel wrote:

Hello i have a question about scopes of block
I want to define a block at one time.
But when it get's called it should have the scope (vars ed )
of the calling environement

Example :
------------------------------

class BlockTest

  attr_accessor :myblock

  def process(&block)
    self.myblock = block
  end
end

t = BlockTest.new
t.process {

  "var = #{out_of_scope_var}"
  }

out_of_scope_var = "daniel"
p t.myblock.call

Results in :

blocktest.rb:15: undefined local variable or method `out_of_scope_var'
for main:Object (NameError) from blocktest.rb:19

How can i call the proc so that the out_of_scope_var is known :

result would be :

so i would get :

daniel-wijnands-powerbook58-2:~/jim/vendor/plugins/widget_grid/lib
danielwijnands$ ruby blocktest.rb
"var = daniel"

The following seems to work:

···

#########
class BlockTest
  def process(&block)
    @block=block
  end

  def myblock
    instance_eval{@block}.call
  end
end

out_of_scope_var = "out of scope, me"
t = BlockTest.new
t.process {"var = #{out_of_scope_var}"}

p t.myblock
#=> "var = out of scope, me"
###########
Hope this helps,
Gustav Paul

4

you could add an eval() into your example code, so that:

    t = BlockTest.new
    t.process { "var = #{out_of_scope_var}" }
    out_of_scope_var = "daniel"
    p t.myblock.call

would become:

    t = BlockTest.new
    t.process { "var = #{eval('out_of_scope_var'}" }
    out_of_scope_var = "daniel"
    p t.myblock.call

hope that helps. --noon

daniel wrote:

···

Hello i have a question about scopes of block
I want to define a block at one time.
But when it get's called it should have the scope (vars ed )
of the calling environement

Example :
------------------------------

class BlockTest

  attr_accessor :myblock

  def process(&block)
    self.myblock = block
  end
end

t = BlockTest.new
t.process {

  "var = #{out_of_scope_var}"
  }

out_of_scope_var = "daniel"
p t.myblock.call

Results in :

blocktest.rb:15: undefined local variable or method `out_of_scope_var'
for main:Object (NameError) from blocktest.rb:19

How can i call the proc so that the out_of_scope_var is known :

result would be :

so i would get :

daniel-wijnands-powerbook58-2:~/jim/vendor/plugins/widget_grid/lib
danielwijnands$ ruby blocktest.rb
"var = daniel"

5

Paul Lutus schreef:

Perhaps you will be satisfied that the block receive values from the parent
environment. This is the normal way to solve the problem.

That is how it is solved now, but the proc needs to be flexible.
I call much proc's and i don't now what to pass.
It are not just vars that i want to accessible but also methods ed

Any idea ?

6

Hi --

···

On Mon, 11 Dec 2006, Gustav Paul wrote:

The following seems to work:
#########
class BlockTest
def process(&block)
   @block=block
end

def myblock
   instance_eval{@block}.call

No need for instance_eval there. @block already belongs to self, and
the instance_eval just resets self to self :slight_smile:

David

--
                   David A. Black | dblack@wobblini.net
Author of "Ruby for Rails" [1] | Ruby/Rails training & consultancy [3]
DABlog (DAB's Weblog) [2] | Co-director, Ruby Central, Inc. [4]
[1] Ruby for Rails | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com | [4] http://www.rubycentral.org

7

Gustav Paul schreef:

The following seems to work:
#########
class BlockTest
  def process(&block)
    @block=block
  end

  def myblock
    instance_eval{@block}.call
  end
end

out_of_scope_var = "out of scope, me"
t = BlockTest.new
t.process {"var = #{out_of_scope_var}"}

p t.myblock
#=> "var = out of scope, me"
###########
Hope this helps,
Gustav Paul

Hi paul, i know that's works, but i need it slightly differtent
because you set out_of_scope_var before you create the block
I want it to be accessible when you set it after you create the block
With your method it is in the scope of the block
I want the block to have access to the scope when you call it
So this should work :

class BlockTest
  def process(&block)
    @block=block
  end
  def myblock
    instance_eval{@block}.call
  end
end

t = BlockTest.new
t.process {"var = #{out_of_scope_var}"}

out_of_scope_var = "out of scope, me"
p t.myblock

But that gives :

blocktest.rb:40: undefined local variable or method `out_of_scope_var'
for main:Object (NameError)
        from blocktest.rb:34:in `myblock'
        from blocktest.rb:45

:frowning: thanks anyway :slight_smile:

8

oops, i forgot to put the closing paren. should be:

    t.process { "var = #{eval('out_of_scope_var')}" }

--noon

9

daniel wrote:

Paul Lutus schreef:

Perhaps you will be satisfied that the block receive values from the
parent environment. This is the normal way to solve the problem.

That is how it is solved now, but the proc needs to be flexible.
I call much proc's and i don't now what to pass.
It are not just vars that i want to accessible but also methods ed

Any idea ?

Use instance variables.

···

-------------------------------------

#!/usr/bin/ruby -w

class BlockTest
   attr_accessor :val
   attr_accessor :myblock
   def process(&block)
      self.myblock = block
   end
end

t = BlockTest.new
t.val = "Daniel"
t.process {
   "var = #{t.val}"
}

p t.myblock.call

-------------------------------------

I understand this is not a particularly pretty example, it is just meant to
show one approach.

--
Paul Lutus
http://www.arachnoid.com

10

dblack@wobblini.net wrote:

Hi --

The following seems to work:
#########
class BlockTest
def process(&block)
@block=block
end

def myblock
instance_eval{@block}.call

No need for instance_eval there. @block already belongs to self, and
the instance_eval just resets self to self :slight_smile:

David

LOL!
doh!
:-]

···

On Mon, 11 Dec 2006, Gustav Paul wrote: