"Local variable within code blocks do not interfere with those outside the block"

I read this in a book.

" In Ruby 1.9, however, local variables used within code blocks will not
interfere with local variables located outside of the block."

I don’t know if my code is wrong, but it looks to me like the local
variable inside the code block DOES interfere with the local variable
(with the same name) outside the code block.

x = [1, 2, 3, 4, 5]
var = 1

x.each do
|number| (var = 10)
end

puts var

=> 10


Or do I not understand the concept? I’m using 1.9.2

Thanks guys!

On Tue, May 24, 2011 at 10:45 AM, Kaye Ng [email protected] wrote:

x.each do
|number| (var = 10)
end

puts var

It’s affecting var because of the assignment, and because it’s not an
argument to the block. You might find
http://ruby.runpaint.org/closures#block-local-variables useful to read
through. Also consider this:

a = 1; [2].each { |x| p a }; a #=> 1; 1
a = 1; [2].each { |x| a = 10; p a }; a #=> 10; 10
a = 1; [2].each { |a| p a }; a #=> 2; 1
a = 1; [2].each { |a| p a; a = 10; p a }; a #=> 2; 10; 1

And with block-local variables in 1.9:

a = 1; [2].each { |;a| p a; }; a #=> nil; 1
a = 1; [2].each { |;a| p a; a = 2; p a }; a #=> nil; 2; 1

On Tue, May 24, 2011 at 11:07 AM, Adam P. [email protected]
wrote:

a = 1; [2].each { |a| p a }; a #=> 2; 1

Important to note that this differs from 1.8:

RUBY_VERSION #=> 1.9.2
a = 1; [2].each { |a| p a }; a #=> 2; 1

RUBY_VERSION #=> 1.8.7
a = 1; [2].each { |a| p a }; a #=> 2; 2

On Tue, May 24, 2011 at 06:45:10PM +0900, Kaye Ng wrote:

var = 1

x.each do
|number| (var = 10)
end

puts var

Others are handling your question well enough, but I have a comment.

It is more idiomatically Rubyish to format your block like this:

x.each do |number|
  var = 10
end

. . . rather than like this:

x.each do
       |number| (var = 10)
     end

I would find the latter style (your version) much more difficult to read
for complex code samples, and I suspect I am not alone in that.

Hi Adam. There’s only one thing I don’t understand:

a = 1; [2].each { |;a| p a; }; a #=> nil; 1
a = 1; [2].each { |;a| p a; a = 2; p a }; a #=> nil; 2; 1

This is the first time I’ve seen a variable passed into a code block
with a semicolon preceding it
|;a|
and also semicolon following the variable
p a;

I’m not sure what it does nor do I understand its significance. =)

Thanks!

Thanks also to Chad P.!!!

On Thu, May 26, 2011 at 8:42 AM, Kaye Ng [email protected] wrote:

I’m not sure what it does nor do I understand its significance. =)

Mateusz has already explained it, but if you need more, you can visit
the
URL I gave just before the code in my post:

http://ruby.runpaint.org/closures#block-local-variables

W dniu 11-05-26 09:42, Kaye Ng pisze:

This is the first time I’ve seen a variable passed into a code block
with a semicolon preceding it
|;a|
This makes the variable’s scope local to block (so when you change it in
block it doesn’t change outside of it).
All the variables before semicolon can be yielded to block by method and
variables after the semicolon are local to block.
I think it was introduced in 1.9, but I’m not really sure about that.
and also semicolon following the variable
p a;
This one just marks the end of statement.
Hope my explanation helps.

Cheers,
Matt

Here x is a variable(array_variable) it contains 5 elements

x = [1,2,3,4,5]

x.each do |r|{puts “#{r}”}
end

=> the result like this order
1
2
3
4
5

This code print x.length time print var= 10

x.each do |r|{
var = 10
puts “#{var}”}
end

=> the result like this order
10
10
10
10
10

But you gave
x.each do |r|{
var = 10
}
end
puts “#{var}”

=> then the x.lenth’th last var value is printed here, the the reason u
got ten value

10

On Thu, May 26, 2011 at 10:20 AM, Bala TS [email protected]
wrote:

10

But you gave
x.each do |r|{
var = 10
}
end
puts “#{var}”

In addition to the syntax errors, you will find this happens:

NameError: undefined local variable or method `var’ for main:Object

var is local to the block. Because of that, it doesn’t accurately
explain
the problem.

On Thu, May 26, 2011 at 4:20 AM, Bala TS [email protected] wrote:

2
3
4
5

I’ve never seen code like this in Ruby. In fact, I get a syntax error
when I try to run this code:

untitled:2: syntax error, unexpected tSTRING_BEG, expecting keyword_do
or ‘{’ or ‘(’
x.each do |r|{puts “#{r}”}
^
untitled:2: syntax error, unexpected ‘}’, expecting keyword_end

I got the point if you try like this way
Here x is a variable(array_variable) it contains 5 elements

x = [1,2,3,4,5]

x.each do |r|
puts “#{r}”
end

=> the result like this order
1
2
3
4
5

This code print x.length time print var= 10

x.each do |r|
var = 10
puts “#{var}”
end

=> the result like this order
10
10
10
10
10

But you gave
x.each do |r|
var = 10
end
puts “#{var}”

x=[1,2,3,4,5]
x.each do |r|
@var = 10
end
puts “#{@var}”

=> then the x.lenth’th last var value is printed here, the the reason u
got ten value

10

On Thu, May 26, 2011 at 06:20:14PM +0900, Bala TS wrote:

Here x is a variable(array_variable) it contains 5 elements

x = [1,2,3,4,5]

x.each do |r|{puts “#{r}”}
end

This code is not correct – and furthermore, the interpoation syntax you
are using is unnecessary. Try this:

x.each {|r| puts r }

The block variable should be identified inside the opening of the
block, and when using braces you do not need “do” and “end”.
Alternatively, if you want to use “do” and “end”, you do not need
braces:

x.each do |r|
  puts r
end

The only reason to use the interpolation syntax here is if you want to
output more than just the contents of the block variable:

x.each {|r| puts "At #{Time.now}, r contains #{r}."; sleep 3 }
At Thu May 26 11:37:25 -0600 2011, r contains 1.
At Thu May 26 11:37:28 -0600 2011, r contains 2.
At Thu May 26 11:37:31 -0600 2011, r contains 3.
At Thu May 26 11:37:34 -0600 2011, r contains 4.
At Thu May 26 11:37:37 -0600 2011, r contains 5.
=> [1, 2, 3, 4, 5]

I have jpg file Here the results are available(screen shot)

by
bala(bdeveloper01)

I got the result

please check it.

by
Bala Ts

On Thu, May 26, 2011 at 11:11 PM, Bala TS [email protected]
wrote:

Posted via http://www.ruby-forum.com/.

r.to_s is equal to “#{r}”, but more straightforward. So when you want to
convert something to a string, it is better to use its to_s method.

The puts method, though, invokes the to_s method on the object before it
outputs it. So when you are sending an object to puts, you don’t need to
worry about whether it is a string at all.

puts “#{r}” # so rather than this
puts r # instead use this

Josh C. wrote in post #1001405:

On Thu, May 26, 2011 at 11:11 PM, Bala TS [email protected]
wrote:

Posted via http://www.ruby-forum.com/.

r.to_s is equal to “#{r}”, but more straightforward. So when you want to
convert something to a string, it is better to use its to_s method.

The puts method, though, invokes the to_s method on the object before it
outputs it. So when you are sending an object to puts, you don’t need to
worry about whether it is a string at all.

puts “#{r}” # so rather than this
puts r # instead use this

If you want to give some name string then
puts r #is not work
puts “value:#{r}”

=> result should come like this format

value:1
value:2
value:3
value:4
value:5

like this way

by
bala(bdeveloper01)

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