[TxMt] Re: run_script.rb

[James Gray]

On Aug 24, 2008, at 10:12 PM, Charles Turner wrote:

> On Sun, 24 Aug 2008 20:08:48 -0500, James Gray wrote:
>> We need something that works in both places, so we need to check for
>> the new 1.9 method lines and map() over it instead, if present.  The
>> code would be something like:
>>
>>   str.send(str.respond_to?(:lines) ? :lines, :to_s).map { … }
>>
>> Hope that helps.
>
> Hi James-
>
> Thanks for your suggestion. The solution is a bit tricky, though. I
> think I have to test for String's support of :map in 1.8, because
> :each_line is supported in both 1.8 and 1.9.
>
> In 1.8, you can do:                   a.map
> but in 1.9, I think you have to do:   a.each_line.to_a.map

You didn't read my code very well.  Please scroll up and have another  
look.  :)

I didn't use each_line() because it is available in both versions.  I  
used the new lines() method, added in 1.9:

$ ruby_dev -ve 'puts "one\ntwo".lines.map { |l| l.capitalize }'
ruby 1.9.0 (2008-03-01 revision 15664) [i686-darwin9.2.0]
One
Two

> The next trick is sending a symbol. It looks like in 1.8 you can say
> "a.send(:map)", but the equivalent "a.send(:each_line.to_a.map)" isn't
> a valid symbol reference in Ruby.

Those two pieces of code are not equivalent.  In the first, you send()  
a Symbol message to the object.  In the second, you are calling to_a()  
on a Symbol.

I promise that send() still works in Ruby 1.9:

$ ruby_dev -ve 'p "one".send(:capitalize)'
ruby 1.9.0 (2008-03-01 revision 15664) [i686-darwin9.2.0]
"One"

> I rewrote your suggestion as:
>
> a.respond_to?(:map) ? a.map : a.each_line.to_a.map do |line| print  
> line
> end
>
> which works for 1.9, but doesn't in 1.8, I think because of the
> conditional's relation the "do" block.

The reason it works in 1.9 is that the standard enumerator library was  
moved into the core.  With this move came the enhancement that most  
iterators now return an Enumerable::Enumerator when called without a  
block.  Thus, in 1.9, it is legal to call map() without a block as you  
do above.  The same is not legal in 1.8.

Hope that answers some of your questions.

James Edward Gray II