Issue #5478 has been updated by Alexey Muranov.


What about simply { :a, :b, :c } ?  It should be obvious to Ruby that this is not a hash.

In fact, how about specifying that internally Set is a form of Hash, and to have a lossless conversion Set->Hash->Set? I do not know the current implementation of Set, but the most natural in my opinion would be the following:
{ :a => nil, :b => nil, :c => nil } # is the set of { :a, :b, :c }.

How about making Ruby interpret { :a, :b, :c => 1 }  as an alternative form of { :a => nil, :b => nil, :c => 1}, and view Set as a simplified Hash, where all values are nil?
That is, make ruby understand that { :a, :b, :c => 1 } is a hash, but  { :a, :b, :c } is a Set (which inherits from Hash).
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Feature #5478: import Set into core, add syntax
http://redmine.ruby-lang.org/issues/5478

Author: Konstantin Haase
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 3.0


=begin
A set is a central data structure. However, a lot of Ruby developers use arrays for situations where it would be more reasonable to use a set. One reason for that is that it is way easier to use Array then Set at the moment, another one is that developers are simply not aware it exists.

I propose moving Set from the stdlib to core and possibly add a syntax or a method on array for creating Set literals.

First class syntax suggestions:

    <1, 2, 3>  # might be tricky to parse
    #[1, 2, 3] # would collide with comments
    $[1, 2, 3]
    ${1, 2, 3}

Method suggestions:

    ~[1, 2, 3]
    +[1, 2, 3]

Whitespace separated String Sets could look like this:

    %w<foo bar blah> # creates an array at the moment 
    #w[foo bar blah] # would collide with comments
    $w[foo bar blah] # would collide with sending :[] to $w
    $w{foo bar blah}

    ~%w[foo bar blah] # not really shorter than using an array with strings
    +%w[foo bar balh] # not really shorter than using an array with strings

Maybe it's ok to not have a whitespace separated syntax, I'm just brainstorming here.

The issue with the method approach is that it would create an Array to send the message to first.

I favor the <1, 2, 3> syntax, possibly without the ability to create a whitespace separated version.

I'd be willing to work on a patch not only for MRI but also for JRuby and Rubinius if you would consider this to be useful.
Although I would need help with the parser.
=end



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