From: David MacMahon <davidm@...>
Date: 2013-08-17T12:03:16-07:00
Subject: [ruby-core:56697] Re: [ruby-trunk - Feature #8772] Hash alias #|	merge, and the case for Hash and Array polymorphism

Does Ruby even support compound operators like "<<|" and "<<&"?

Dave

On Aug 17, 2013, at 11:48 AM, alexeymuranov (Alexey Muranov) wrote:

> 
> Issue #8772 has been updated by alexeymuranov (Alexey Muranov).
> 
> 
> =begin
> How about (({Hash#<<})) for (({#merge!})) (plus, maybe extra functionality suggested by Thomas), (({Hash#<<|})) for (({#reverse_merge!})) (plus extra), (({Hash#<<&})) for (({#merge!})) which only touches existing keys (plus extra):
> 
>  { :a => 1, :b => 2 } <<  { :b => 1, :c => 2 }  # => { :a => 1, :b => 1, :c => 2 }
> 
>  { :a => 1, :b => 2 } <<| { :b => 1, :c => 2 }  # => { :a => 1, :b => 2, :c => 2 }
> 
>  { :a => 1, :b => 2 } <<& { :b => 1, :c => 2 }  # => { :a => 1, :b => 1 }
> 
> Everything changes the receiver in place.
> 
> (I am not opening a new ticket for this because i am not yet sure i am excited about quite different behavior of #<< in different classes.)
> =end
> 
> ----------------------------------------
> Feature #8772: Hash alias #| merge, and the case for Hash and Array polymorphism
> https://bugs.ruby-lang.org/issues/8772#change-41228
> 
> Author: trans (Thomas Sawyer)
> Status: Open
> Priority: Normal
> Assignee: 
> Category: core
> Target version: current: 2.1.0
> 
> 
> Ideally Hash and Array would be completely polymorphic in every manner in which it is possible for them to be so. The reason for this is very simple. It makes a programmer's life easier. For example, in a recent program I was working on, I had a list of keyboard layouts.
> 
>  layouts = [layout1, layout2, layout3]
> 
> Later I realized I wanted to identify them by a label not an index. So...
> 
>  layouts = {:foo => layout1, :bar => layout2, :baz => layout3}
> 
> Unfortunately this broke my program in a number of places, and I had to go through every use of `layouts` to translate what was an Array call into a Hash call. If Array and and Hash were more polymorphic I would have only had to adjust the places were I wanted to take advantage of the Hash. Ideally almost nothing should have actually broken. 
> 
> The achieve optimal polymorphism between Hash and Array is to treat a Hash's keys as indexes and its values as as the values of an array. e.g.
> 
>  a = [:a,:b,:c]
>  h = {0=>:a,1=>:b,2=>:c}
>  a.to_a  #=> [:a,:b,:c]
>  h.to_a  #=> [:a,:b,:c]
> 
> Of course the ship has already sailed for some methods that are not polymorphic, in particular #each. Nonetheless it would still be wise to try to maximize the polymorphism going forward. (Perhaps even to be willing to take a bold leap in Ruby 3.0 to break some backward compatibility to improve upon this.)
> 
> In the mean time, let us consider what it might mean for Hash#+ as an alias for #merge, *if the above were so*:
> 
>  ([:a,:b] + [:c,:d]).to_a             => [:a,:b,:c,:d]
>  ({0=>:a,1=>:b} + {2=>:c,3=>:d}).to_a => [:a,:b,:c,:d]
> 
>  ([:a,:b] + [:a,:b]).to_a             => [:a,:b,:a,:b]
>  ({0=>:a,1=>:b} + {0=>:a,1=>:b}).to_a => [:a,:b]
> 
> Damn! So it appears that #+ isn't the right operator. Let's try #| instead.
> 
>  ([:a,:b] | [:c,:d]).to_a             => [:a,:b,:c,:d]
>  ({0=>:a,1=>:b} | {2=>:c,3=>:d}).to_a => [:a,:b,:c,:d]
> 
>  ([:a,:b] | [:a,:b]).to_a             => [:a,:b]
>  ({0=>:a,1=>:b} | {0=>:a,1=>:b}).to_a => [:a,:b]
> 
> Bingo. So I formally stand corrected. The best alias for merge is #| not #+. 
> 
> Based on this line of reasoning I formally request the Hash#| be an alias of Hash#merge.
> 
> P.S. Albeit, given the current state of polymorphism between Ruby's Array and Hash, and the fact that it will probably never be improved upon, I doubt it really matters which operator is actually used.
> 
> 
> 
> -- 
> http://bugs.ruby-lang.org/