From: Kristof Bastiaensen <kristof@...>
Date: 2004-06-20T02:08:30+09:00
Subject: Re: [RCR] More enumerator functionality

On Sat, 19 Jun 2004 19:28:28 +0900, Michael Neumann wrote:

> On Fri, Jun 18, 2004 at 10:13:25PM +0900, Kristof Bastiaensen wrote:
>> On Fri, 18 Jun 2004 21:28:45 +0900, Michael Neumann wrote:
>> 
>> [...]
>>
>> > 
>> > That's a more general form, as after the "lazy", all Enumerable
>> > operations do not create intermediate arrays. Of course, it's very slow
>> > compared to the non-lazy methods (Generator uses continuations).
>> > 
>> > 
>> That's interesting.
>> If I am correct, your collect_lazy and lazy.collect behaves the same as
>> enum_for with a block. Your select_lazy and lazy.select the same as
>> enum_if.
> 
> I don't know what enum_for is doing, but select_lazy is the same as
> enum_if, only it's implementation is very different.
> 

Currently enum_for (and its alias to_enum) creates an enumerable
that uses a different method than each.  For example:

  require "enumerator"
  str = "xyz"

  enum = str.enum_for(:each_byte)
  a = enum.map {|b| '%02x' % b } #=> ["78", "79", "7a"]

My proposal is that enum_for can take a block, so it can
do a custom transformation on the data:

  data = [2, 3, 6]
  powers = data.enum_for { |i| i * i } #"each" implied
  powers.to_a
  => [4, 9, 36]

  data << 7
  powers.to_a
  => [4, 9, 36, 49]

If I am not mistaken this is the same as your collect_lazy.

Regards,
Kristof