Same variable name used in block and local question

ruby-talk
1

Can anybody help me here, TIA!!

This is the code. I expect to see the string "Afterward:turkey", but
why am I getting "Afterward:camel"? |animal| parameter in a block
should be temporary inside the block, right??

Code:

···

----------
animal = "turkey"

puts "Original:" + animal
puts

["cow","camel"].each { |animal| puts "in block:" + animal }

puts
puts "Afterwards:" + animal

Output:
-----------
Original:turkey

in block:cow
in block:camel

Afterwards:camel

2

rubyrus wrote:

Can anybody help me here, TIA!!

This is the code. I expect to see the string "Afterward:turkey", but
why am I getting "Afterward:camel"? |animal| parameter in a block
should be temporary inside the block, right??

No, it isn't because it was defined outside the block. It's used in cases
like

count = 0
arr.each { count += 1 }
puts "count=#{count}"

If you want to keep it local you must not define it in the surrounding
scope.

Kind regards

    robert

3

Hi --

Can anybody help me here, TIA!!

This is the code. I expect to see the string "Afterward:turkey", but
why am I getting "Afterward:camel"? |animal| parameter in a block
should be temporary inside the block, right??

Code:
----------
animal = "turkey"

puts "Original:" + animal
puts

["cow","camel"].each { |animal| puts "in block:" + animal }

puts
puts "Afterwards:" + animal

Output:
-----------
Original:turkey

in block:cow
in block:camel

Afterwards:camel

Block parameters actually use assignment semantics, so if a variable
already exists, it gets assigned to. The animal in the pipes is the
same as the animal before the block. If you use a new local variable,
it will come into being just for the block.

Before a hundred-message thread gets spawned, let me add that yes,
it's going to change in 2.0 :slight_smile: I'm actually one of the few people
who like it the way it is, but Matz has said that he considers it a
design mistake and wants to change it.

David

···

On Tue, 28 Feb 2006, rubyrus wrote:

--
David A. Black (dblack@wobblini.net)
Ruby Power and Light (http://www.rubypowerandlight.com)

"Ruby for Rails" chapters now available
from Manning Early Access Program! http://www.manning.com/books/black

4

Hi --

rubyrus wrote:

Can anybody help me here, TIA!!

This is the code. I expect to see the string "Afterward:turkey", but
why am I getting "Afterward:camel"? |animal| parameter in a block
should be temporary inside the block, right??

No, it isn't because it was defined outside the block. It's used in cases
like

count = 0
arr.each { count += 1 }
puts "count=#{count}"

If you want to keep it local you must not define it in the surrounding
scope.

I think that's a different thing, though, from the parameter
semantics. As I understand it, in 2.0 things would work like this:

   count = 0
   other = "zero"
   [1,2,3].each {|other| count += 1 }

   # count is now 3
   # other is still "zero"

I may be getting it wrong... but I think the scoping of parameter
variables and other block variables is going to diverge.

David

···

On Tue, 28 Feb 2006, Robert Klemme wrote:

--
David A. Black (dblack@wobblini.net)
Ruby Power and Light (http://www.rubypowerandlight.com)

"Ruby for Rails" chapters now available
from Manning Early Access Program! http://www.manning.com/books/black

5

dblack@wobblini.net wrote:

Hi --

rubyrus wrote:

Can anybody help me here, TIA!!

This is the code. I expect to see the string "Afterward:turkey",
but why am I getting "Afterward:camel"? |animal| parameter in a
block should be temporary inside the block, right??

No, it isn't because it was defined outside the block. It's used in
cases like

count = 0
arr.each { count += 1 }
puts "count=#{count}"

If you want to keep it local you must not define it in the
surrounding scope.

I think that's a different thing, though, from the parameter
semantics. As I understand it, in 2.0 things would work like this:

Is there a difference with regard to scope between

(1..10).each {|foo| }

and

(1..10).each { foo = 1 }

? I think in both cases foo is limited to the block:

16:51:56 [~]: ruby -e 'def f() (1..5).each {|foo|}; foo end; f'
-e:1:in `f': undefined local variable or method `foo' for main:Object
(NameError)
        from -e:1
16:51:59 [~]: ruby -e 'def f() (1..5).each {foo=1}; foo end; f'
-e:1:in `f': undefined local variable or method `foo' for main:Object
(NameError)
        from -e:1
16:52:04 [~]:

Note, I'm not talking about Ruby 2.

   count = 0
   other = "zero"
   [1,2,3].each {|other| count += 1 }

   # count is now 3
   # other is still "zero"

I may be getting it wrong... but I think the scoping of parameter
variables and other block variables is going to diverge.

That's why I stick to the status quo - I lost track of this discussion
somewhere. But I trust Matz to do it properly. At least all relevant
arguments seem to have been exchanged. :slight_smile:

Kind regards

    robert

···

On Tue, 28 Feb 2006, Robert Klemme wrote:

6

Hi --

···

On Wed, 1 Mar 2006, Robert Klemme wrote:

dblack@wobblini.net wrote:

Hi --

On Tue, 28 Feb 2006, Robert Klemme wrote:

rubyrus wrote:

Can anybody help me here, TIA!!

This is the code. I expect to see the string "Afterward:turkey",
but why am I getting "Afterward:camel"? |animal| parameter in a
block should be temporary inside the block, right??

No, it isn't because it was defined outside the block. It's used in
cases like

count = 0
arr.each { count += 1 }
puts "count=#{count}"

If you want to keep it local you must not define it in the
surrounding scope.

I think that's a different thing, though, from the parameter
semantics. As I understand it, in 2.0 things would work like this:

Is there a difference with regard to scope between

(1..10).each {|foo| }

and

(1..10).each { foo = 1 }

? I think in both cases foo is limited to the block:

I guess I had the impression that what puzzled the OP was that using a
variable as a block parameter (as opposed to just using it in the
block) was trampling the outer variable. Anyway, as you say, all
perspectives have been accounted for (many times, counting the
archives :slight_smile:

David

--
David A. Black (dblack@wobblini.net)
Ruby Power and Light (http://www.rubypowerandlight.com)

"Ruby for Rails" chapters now available
from Manning Early Access Program! http://www.manning.com/books/black