From: 7rans <transfire@...>
Date: 2009-08-31T01:08:35+09:00
Subject: Re: #map, #select semantics



On Aug 29, 9:25 am, Yukihiro Matsumoto <m...@ruby-lang.org> wrote:
> Hi,
>
> In message "Re: #map, #select semantics"
>     on Sat, 29 Aug 2009 21:32:21 +0900, 7rans <transf...@gmail.com> writes:
>
> |Let's say we have
> |
> |  [[:a,1], [:b,2]].map{ |(k,v)| [k, v+1] }  #=> [[:a,2], [:b,3]]
> |
> |We might have something like:
> |
> |[[:a,1], [:b,2]].using({}).map{|(k,v)| [k, v+1]}     #=> {:a=>2, :b=>3}
>
> [[:a,1], [:b,2]].inject({}){|h,(k,v)| h[k]=v+1; h}     #=> {:a=>2, :b=>3}

Ok. There are lots of ways to do it. Often I actually will use the
faster:

  h={};[[:a,1], [:b,2]].each{|(k,v)| h[k]=v+1}; h

But the ideal was to also achieve:

  {:a=>1, :b=>2}.map{ |k,v| [k, v+1] }  #=> {:a=>2, :b=>3}

Which is far more clear then the alternatives (and easily converted to
an Array with #to_a). The idea of #using is just icing on the cake,
but is itself clearer than #inject (or the new #each_with_object),
both of which strike me as primarily inventions to make up for the
lack of the above, which I imagine represents a large chunk of the use
cases.

However, it does break backwards compatibility, so I don't expect it's
uptake irregardless of it's merits.