[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:

>=20
> Issue #8772 has been updated by alexeymuranov (Alexey Muranov).
>=20
>=20
> =3Dbegin
> 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):
>=20
>  { :a =3D> 1, :b =3D> 2 } <<  { :b =3D> 1, :c =3D> 2 }  # =3D> { :a =3D>=
 1, :b =3D> 1, :c =3D> 2 }
>=20
>  { :a =3D> 1, :b =3D> 2 } <<| { :b =3D> 1, :c =3D> 2 }  # =3D> { :a =3D>=
 1, :b =3D> 2, :c =3D> 2 }
>=20
>  { :a =3D> 1, :b =3D> 2 } <<& { :b =3D> 1, :c =3D> 2 }  # =3D> { :a =3D>=
 1, :b =3D> 1 }
>=20
> Everything changes the receiver in place.
>=20
> (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.)
> =3Dend
>=20
> ----------------------------------------
> Feature #8772: Hash alias #| merge, and the case for Hash and Array =
polymorphism
> https://bugs.ruby-lang.org/issues/8772#change-41228
>=20
> Author: trans (Thomas Sawyer)
> Status: Open
> Priority: Normal
> Assignee:=20
> Category: core
> Target version: current: 2.1.0
>=20
>=20
> 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.
>=20
>  layouts =3D [layout1, layout2, layout3]
>=20
> Later I realized I wanted to identify them by a label not an index. =
So...
>=20
>  layouts =3D {:foo =3D> layout1, :bar =3D> layout2, :baz =3D> layout3}
>=20
> 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.=20
>=20
> 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.
>=20
>  a =3D [:a,:b,:c]
>  h =3D {0=3D>:a,1=3D>:b,2=3D>:c}
>  a.to_a  #=3D> [:a,:b,:c]
>  h.to_a  #=3D> [:a,:b,:c]
>=20
> 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.)
>=20
> In the mean time, let us consider what it might mean for Hash#+ as an =
alias for #merge, *if the above were so*:
>=20
>  ([:a,:b] + [:c,:d]).to_a             =3D> [:a,:b,:c,:d]
>  ({0=3D>:a,1=3D>:b} + {2=3D>:c,3=3D>:d}).to_a =3D> [:a,:b,:c,:d]
>=20
>  ([:a,:b] + [:a,:b]).to_a             =3D> [:a,:b,:a,:b]
>  ({0=3D>:a,1=3D>:b} + {0=3D>:a,1=3D>:b}).to_a =3D> [:a,:b]
>=20
> Damn! So it appears that #+ isn't the right operator. Let's try #| =
instead.
>=20
>  ([:a,:b] | [:c,:d]).to_a             =3D> [:a,:b,:c,:d]
>  ({0=3D>:a,1=3D>:b} | {2=3D>:c,3=3D>:d}).to_a =3D> [:a,:b,:c,:d]
>=20
>  ([:a,:b] | [:a,:b]).to_a             =3D> [:a,:b]
>  ({0=3D>:a,1=3D>:b} | {0=3D>:a,1=3D>:b}).to_a =3D> [:a,:b]
>=20
> Bingo. So I formally stand corrected. The best alias for merge is #| =
not #+.=20
>=20
> Based on this line of reasoning I formally request the Hash#| be an =
alias of Hash#merge.
>=20
> 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.
>=20
>=20
>=20
> --=20
> http://bugs.ruby-lang.org/