Issue #5478 has been updated by Alexey Muranov.


Jos Backus wrote:
> How would one represent an empty Set?    
> '{}' can't be used as it would be ambiguous.

Good point.  Need to think about this.  I would be in favor of using `{}` for the empty set and `Hash::new`, or `Hash[]`, or `{}.to_hash` for the empty hash.  To keep partial compatibility, Set can convert itself to Hash if a `#[]` or `#[]=` method is called on it.  Actually, can it?  Can an object replace itself with an object of another class in Ruby?  Also, `{}` can be an object of some common ancestor class of Hash and Set, if this can help.

I think it should be possible to use a single class as both Set and Hash, but having set methods and hash methods both defined on the same object somehow seems strange to me.
----------------------------------------
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



-- 
http://redmine.ruby-lang.org