Implementing each and <=>

ruby-talk
1

I have a data model and would like to let it be Enumerable. I want to
confirm if this is the way of implementing each and <=> :

    def each
      @list.each { |item| yield item }
    end

    def <=>(other)
      @list <=> other
    end

(let's just assume that @list is an array)

Thanks.

···

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

2

Ruby Rabbit schrieb:

I have a data model and would like to let it be Enumerable. I want to
confirm if this is the way of implementing each and <=> :

    def each
      @list.each { |item| yield item }
    end

    def <=>(other)
      @list <=> other
    end

(let's just assume that @list is an array)

Thanks.

i would define each like this:
   def each(&blk)
     @list.each(&blk)
   end

3

<=> would normally apply to items in your list, not to the container itself.

···

On Jan 13, 2009, at 1:08 PM, Ruby Rabbit wrote:

I have a data model and would like to let it be Enumerable. I want to
confirm if this is the way of implementing each and <=> :

...

  def <=>(other)
     @list <=> other
   end

4

Ruby Rabbit wrote:

    def <=>(other)
      @list <=> other
    end

Perhaps you mean something like this:

  include Comparable
  def <=>(other)
    @list <=> other.list # or some other way to order them
  end

Making your objects Comparable is distinct from making them Enumerable.

···

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5

badboy wrote:

Ruby Rabbit schrieb:

(let's just assume that @list is an array)

Thanks.

i would define each like this:
   def each(&blk)
     @list.each(&blk)
   end

okay, i forgot to mention that I was wondering whether the
easiest/cleanest way was to use a send somehow?

    def each
      @list.send
    end

Actually, since the ruby source is in 'C' one can't check it to see
examples. I searched a lot but came up with nothing.

Thanks.

···

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6

Dave Thomas wrote:

···

On Jan 13, 2009, at 1:08 PM, Ruby Rabbit wrote:

I have a data model and would like to let it be Enumerable. I want to
confirm if this is the way of implementing each and <=> :

...

  def <=>(other)
     @list <=> other
   end

<=> would normally apply to items in your list, not to the container
itself.

That's whats confusing me. How would i put it?

I am putting in the <=> so this class might be more useful to others. I
haven't got around to using it myself. (I have a base class
ListDataModel with minimal methods and wanted to make it as useful as
possible).
--
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7

Brian Candler wrote:

Ruby Rabbit wrote:

    def <=>(other)
      @list <=> other
    end

Perhaps you mean something like this:

  include Comparable
  def <=>(other)
    @list <=> other.list # or some other way to order them
  end

Making your objects Comparable is distinct from making them Enumerable.

I was thinking that including Comparable would give users the ability to
sort the existing model in various ways.

I was wrong there, since it clearly is a comparison with another model.
That is not something likely. My bad. Thanks, Brian.

···

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8

Ruby Rabbit schrieb:

badboy wrote:

Ruby Rabbit schrieb:

(let's just assume that @list is an array)

Thanks.

i would define each like this:
   def each(&blk)
     @list.each(&blk)
   end

okay, i forgot to mention that I was wondering whether the easiest/cleanest way was to use a send somehow?

    def each
      @list.send
    end

Actually, since the ruby source is in 'C' one can't check it to see examples. I searched a lot but came up with nothing.

Thanks.

I don't think that using send is easier/cleaner
using @list.each(&blk) is nothing else than sending the message "each" to @list with blk as a block parameter

9

Is there sume useful comparison for comparing two different data models
with each other? If not, then don't define <=>.

--Ken

···

On Tue, 13 Jan 2009 15:30:20 -0500, Ruby Rabbit wrote:

I am putting in the <=> so this class might be more useful to others. I
haven't got around to using it myself. (I have a base class
ListDataModel with minimal methods and wanted to make it as useful as
possible).

--
Chanoch (Ken) Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/

10

No. This won't work. Send is just a method for calling methods, and
unless you pass it a method name and all relevant arguments, it won't
know what message to send.

Thus, you'll be at

def each &blk
  @list.send :each, &blk
end

and it's easier to do

def each &blk
  @list.each &blk
end

--Ken

···

On Tue, 13 Jan 2009 14:15:58 -0500, Ruby Rabbit wrote:

badboy wrote:

Ruby Rabbit schrieb:

(let's just assume that @list is an array)

Thanks.

i would define each like this:
   def each(&blk)
     @list.each(&blk)
   end

okay, i forgot to mention that I was wondering whether the
easiest/cleanest way was to use a send somehow?

    def each
      @list.send
    end

--
Chanoch (Ken) Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/

11

Thus, you'll be at

def each &blk
  @list.send :each, &blk
end

and it's easier to do

def each &blk
  @list.each &blk
end

--Ken

thanks, (I did forget to put the :each in the lines i put)

Is there sume useful comparison for comparing two different data models
with each other? If not, then don't define <=>.

No, not at all. Thanks again.

···

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