Question about magic enumerators in > 1.8

ruby-talk
1

Hi --

Can someone jog my memory, and/or enlighten me, as to what a case
would be where it's useful to have:

   array.map

return an Enumerator? I can't seem to come up with an example where:

   array.map.anything

is different from

   array.anything

Thanks --

David

···

--
http://www.rubypowerandlight.com => Ruby/Rails training & consultancy
http://www.manning.com/black => RUBY FOR RAILS, the Ruby book for
                                                     Rails developers
http://dablog.rubypal.com => D[avid ]A[. ]B[lack's][ Web]log
dblack@wobblini.net => me

2

Well, you can use it to roll the oft-requested map_with_index():

   array.each_with_index.map { |obj, i| .. }

That's not a map() example though, so maybe not what you wanted.

James Edward Gray II

···

On Jul 9, 2006, at 9:03 AM, dblack@wobblini.net wrote:

Hi --

Can someone jog my memory, and/or enlighten me, as to what a case
would be where it's useful to have:

  array.map

return an Enumerator? I can't seem to come up with an example where:

  array.map.anything

is different from

  array.anything

Thanks --

3

return an Enumerator? I can't seem to come up with an example where:

  array.map.anything

is different from

  array.anything

moulon% ./ruby -e '[12].map.with_index {}'
moulon%

moulon% ./ruby -e '[12].with_index {}'
-e:1: undefined method `with_index' for [12]:Array (NoMethodError)
moulon%

p.s.:
:-))))

···

--

Guy Decoux

4

dblack@wobblini.net writes:

Hi --

Can someone jog my memory, and/or enlighten me, as to what a case
would be where it's useful to have:

  array.map

return an Enumerator? I can't seem to come up with an example where:

  array.map.anything

is different from

  array.anything

names.map { |x| x.size }.max, and you don't need an immediate array.

···

Thanks --

David

--
Christian Neukirchen <chneukirchen@gmail.com> http://chneukirchen.org

5

Hi --

···

On Sun, 9 Jul 2006, James Edward Gray II wrote:

On Jul 9, 2006, at 9:03 AM, dblack@wobblini.net wrote:

Hi --

Can someone jog my memory, and/or enlighten me, as to what a case
would be where it's useful to have:

  array.map

return an Enumerator? I can't seem to come up with an example where:

  array.map.anything

is different from

  array.anything

Thanks --

Well, you can use it to roll the oft-requested map_with_index():

array.each_with_index.map { |obj, i| .. }

That's not a map() example though, so maybe not what you wanted.

Right, it isn't :slight_smile: I'm still looking for a map example.

David

--
http://www.rubypowerandlight.com => Ruby/Rails training & consultancy
Ruby for Rails => RUBY FOR RAILS, the Ruby book for
                                                     Rails developers
http://dablog.rubypal.com => D[avid ]A[. ]B[lack's][ Web]log
dblack@wobblini.net => me

6

Hi --

···

On Mon, 10 Jul 2006, Christian Neukirchen wrote:

dblack@wobblini.net writes:

Hi --

Can someone jog my memory, and/or enlighten me, as to what a case
would be where it's useful to have:

  array.map

return an Enumerator? I can't seem to come up with an example where:

  array.map.anything

is different from

  array.anything

names.map { |x| x.size }.max, and you don't need an immediate array.

That's not an example of what I'm asking about, though. There's no
enumerator returned there.

David

--
http://www.rubypowerandlight.com => Ruby/Rails training & consultancy
Ruby for Rails => RUBY FOR RAILS, the Ruby book for
                                                     Rails developers
http://dablog.rubypal.com => D[avid ]A[. ]B[lack's][ Web]log
dblack@wobblini.net => me

7

Contrived example: I know a method I'm about to call iterates thru me with each doing something. It's the last thing it does and what the results of the thing it does rather than myself at the end:

some_method(array.map)

Ok so it's a REALLY contrived example.

···

On Jul 9, 2006, at 10:36 AM, dblack@wobblini.net wrote:

Hi --

On Sun, 9 Jul 2006, James Edward Gray II wrote:

On Jul 9, 2006, at 9:03 AM, dblack@wobblini.net wrote:

Hi --
Can someone jog my memory, and/or enlighten me, as to what a case
would be where it's useful to have:

  array.map
return an Enumerator? I can't seem to come up with an example where:

  array.map.anything
is different from

  array.anything
Thanks --

Well, you can use it to roll the oft-requested map_with_index():

array.each_with_index.map { |obj, i| .. }

That's not a map() example though, so maybe not what you wanted.

Right, it isn't :slight_smile: I'm still looking for a map example.

David

--
http://www.rubypowerandlight.com => Ruby/Rails training & consultancy
Ruby for Rails => RUBY FOR RAILS, the Ruby book for
                                                    Rails developers
http://dablog.rubypal.com => D[avid ]A[. ]B[lack's][ Web]log
dblack@wobblini.net => me