From: "wardrop (Tom Wardrop)" <tom@...>
Date: 2013-11-15T08:57:00+09:00
Subject: [ruby-core:58344] [ruby-trunk - Feature #9108] Hash sub-selections


Issue #9108 has been updated by wardrop (Tom Wardrop).


=begin
I suppose square-bracket syntax is too ambiguous as it collides with many other existing and potential behaviours I didn't consider. A normal method is fine.

I think an appropriate solution would be to amend Hash#select. It currently doesn't take any arguments, so could easily take a list of (({*args})). You could use the optional block to further refine this selection if need be. The same for Hash#reject.

One potential issue though is that Hash#select without any arguments currently returns an enumerator. This could be problematic when doing something like ({hash.select *args})) with an empty array. I think calling Hash#select without arguments should return a copy of the full original Hash, this keeps it somewhat compatible with the existing behaviour of returning an enumerator (given a Hash is an enumerator), while at the same time making it consistent with the new Hash#select(*keys) functionality.

What do you think of changing#select and #reject to support this?
=end
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Feature #9108: Hash sub-selections
https://bugs.ruby-lang.org/issues/9108#change-42942

Author: wardrop (Tom Wardrop)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 


=begin
Hi,

I seem to regularly have the requirement to work on a sub-set of key/value pairs within a hash. Ruby doesn't seem to provide a concise means of selecting a sub-set of keys from a hash. To give an example of what I mean, including how I currently achieve this:

    sounds = {dog: 'woof', cat: 'meow', mouse: 'squeak', horse: 'nay', cow: 'moo'}
    domestic_sounds = sounds.select { |k,v| [:dog, :cat].include? k } #=> {dog: 'woof', cat: 'meow'}

I think a more concise and graceful solution to this would be to allow the Hash#[] method to take multiple arguments, returning a sub-hash, e.g.

    domestic_sounds = sounds[:dog, :cat] #=> {dog: 'woof', cat: 'meow'}

I had a requirement in the current project I'm working on to concatenate two values in a hash. If this proposed feature existed, I could of just done this...

    sounds[:dog, :cat].values.join #=> 'woofmeow'

You could do something similar for the setter also...

    sounds[:monkey, :bat] = 'screech'
    sounds #=> {dog: 'woof', cat: 'meow', mouse: 'squeak', horse: 'nay', cow: 'moo', monkey: 'screech', bat: 'screech'}

Concise, convenient and readable. Thoughts?

=end


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