The question about 'Range' as Condition

ruby-talk
1

Hi All,

I don't know why these two codes of behavior will not be the same,
in my opinion, they are the same logic.

Thanks a lot!

Codes:

···

-------------------------------------------------
arr = [ 'head', 'start', 'body', 'end', 'tail' ]

# test 1
puts 'loop test:'
for i in 0...arr.size
  puts arr[i] if arr[i] =~ /start/ .. arr[i] =~ /end/
end

puts

# test 2
puts 'hard test:'
puts arr[0] if arr[0] =~ /start/ .. arr[0] =~ /end/
puts arr[1] if arr[1] =~ /start/ .. arr[1] =~ /end/
puts arr[2] if arr[2] =~ /start/ .. arr[2] =~ /end/
puts arr[3] if arr[3] =~ /start/ .. arr[3] =~ /end/
puts arr[4] if arr[4] =~ /start/ .. arr[4] =~ /end/
-------------------------------------------------

The output:
----------
loop test:
start
body
end

hard test:
start
----------

- Haibin Shi

2

No, it's not, because you change the number of range operators. A range
operator in an if / unless situation has a built in FlipFlop which will
change the state whenever a change in matching occurs:
http://www.ruby-doc.org/docs/ProgrammingRuby/html/tut_expressions.html#UF

Cheers

robert

···

On Tue, May 7, 2013 at 12:07 PM, Haibin Shi <syunxi@gmail.com> wrote:

Hi All,

I don't know why these two codes of behavior will not be the same,
in my opinion, they are the same logic.

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

3

Hi Robert,

Thanks in advance for your help!

No, it's not, because you change the number of range operators.

But I still do not understand what's the *number* of range operators.

Is the state of flip-flop only be kept within loop ?

Cheers

Haibin

4

No, the state is attached to a single source code location if you will (and
per thread I believe). That's why. In the first case you have 1 instance
in the second multiple.

Cheers

robert

···

On Tue, May 7, 2013 at 6:14 PM, Haibin Shi <syunxi@gmail.com> wrote:

> No, it's not, because you change the number of range operators.
But I still do not understand what's the *number* of range operators.

Is the state of flip-flop only be kept within loop ?

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

5

Hi Robert,

I finally get to know!
Thanks again!

Cheers

Haibin

···

On Wed, May 08, 2013 at 01:31:12AM +0900, Robert Klemme wrote:

On Tue, May 7, 2013 at 6:14 PM, Haibin Shi <syunxi@gmail.com> wrote:

> > No, it's not, because you change the number of range operators.
> But I still do not understand what's the *number* of range operators.
>
> Is the state of flip-flop only be kept within loop ?
>

No, the state is attached to a single source code location if you will (and
per thread I believe). That's why. In the first case you have 1 instance
in the second multiple.

Cheers

robert

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/