[ruby-core:40795] [ruby-trunk - Feature #5478] import Set into core, add syntax

Issue #5478 has been updated by George Koehler.


=begin
Ruby stdlib already has Set::[], a method that creates a literal set.

 irb(main):001:0> require 'set'
 => true
 irb(main):002:0> Set[1, 2, 3]
 => #<Set: {1, 2, 3}>

The proposed syntax <1, 2, 3> might be impossible to parse, because it conflicts with < and > operators. Consider this example:

 def c(*args); args.length; end
 
 p c <1, 2, 3>
 4

Current Ruby (with no set literal syntax) parses this example like so:

 p(c() < 1, 2, (3 >
                4))

If <1, 2, 3> became a set literal, then this example would become ambiguous. No parser would know whether this code has a set literal, or calls < and > operators.
=end

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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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