[ruby-core:65393] [ruby-trunk - Feature #9108] Hash sub-selections

Issue #9108 has been updated by Andrew M.


My personal preference would be for `Hash#select(*args)` and `Hash#reject(*args)`, but if we *really* must maintain backwards compatibility for `Hash#reject` with no args or block then I guess `Hash#select(enum)` and `Hash#reject(enum)` would fine too.

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Feature #9108: Hash sub-selections
https://bugs.ruby-lang.org/issues/9108#change-49192

* Author: Tom Wardrop
* Status: Open
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
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=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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