From: "David A. Black" <dblack@...>
Date: 2009-09-16T04:41:56+09:00
Subject: Re: .map.with_object(3){|v|v+3} #=> 3 Is this a bug?

Hi --

On Wed, 16 Sep 2009, 7stud -- wrote:

> The next call in the method chain is map():
>
>>>> [1,2,3].each.with_object(3).map{|v|v+3}
>
> map takes the value(s) it is sent, converts the value(s), then stores
> the converted value(s) in an array, then the array is returned as the
> final result of the call to map():
>
> result = [1,2,3].each.with_object(3).map do |v, w|
>  puts "#{v} #{w}"
>  v + 3
> end
>
> p result
>
> --output:--
> 1 3
> 2 3
> 3 3
> [4, 5, 6]
>
> That is why you get the result:
>
>>>> [1,2,3].each.with_object(3).map{|v|v+3}
>> => [4, 5, 6]

Except....

   >> [1,2,3].each.with_object("hi!").map{|v| v + 3 }
   => [4, 5, 6]

The map is only binding one of the arguments, and the argument to
with_object is being ignored. (The 3 is hard-coded in the block.)

To make use of it in the map, you'd have to do:

   [1,2,3].each.with_object(3).map{|v,w| v + w }


David

-- 
David A. Black, Director
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