[ruby-core:61475] [ruby-trunk - Feature #5825] Sweet instance var assignment in the object initializer

Issue #5825 has been updated by Tyler Rick.


I would *love* to see this feature in Ruby.  Assigning an argument to an instance variable in a constructor is something that we do in *almost every constructor we write*, so I think this should be made as easy and simple as possible, by adding a little syntactic sugar to the language.

I shouldn't have to repeat myself and type out each argument name ***3 times*** in every constructor I write, for something as mundane as this:

    def initialize(name₁, …)
      @name₂ = name₃
      …
    end

This constant repetition feels inelegant to me and goes against one of the Ruby community's most fundamental values (Don't Repeat Yourself).

This method could be simplified to simply this:

    def initialize(@name, …)
    end

I think CoffeeScript solved this problem quite nicely.  Many constructors in CoffeeScript end up being beautiful, simple one-liners!

    constructor: (@name) ->

And with the rising popularity of CoffeeScript, there are going to be more and more Rubyists not only *wishing* for this but also ***expecting*** this same feature to exist in Ruby as well.  :)

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Here are a few more "votes" for this feature:
* http://stackoverflow.com/questions/10856191/ruby-automatically-set-instance-variable-as-method-argument
* http://stackoverflow.com/questions/9597249/in-ruby-can-i-automatically-populate-instance-variables-somehow-in-the-initializ/10855962
* http://stackoverflow.com/questions/16072965/why-do-method-arguments-not-work-for-assignment

Plus various attempts at removing the duplication from assign variables in constructors, using only pure Ruby:
* http://redsquirrel.com/cgi-bin/dave/dynamic/def_init.html (`def_init :arg1, :arg2`)
* http://blog.jayfields.com/2007/04/ruby-assigning-instance-variables-in.html (`initializer :arg1, :arg2`)
* https://github.com/rubyworks/facets/blob/master/lib/core/facets/kernel/assign.rb (`assign(hash)`)
* https://github.com/sheldonh/magic_options (`magic_initialize` and `magic_options(hash)`)
(But pure Ruby solutions can only go so far, and none of those solutions really solve the problem nicely enough...)

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Feature #5825: Sweet instance var assignment in the object initializer
https://bugs.ruby-lang.org/issues/5825#change-45766

* Author: Gosha Arinich
* Status: Assigned
* Priority: Normal
* Assignee: Yukihiro Matsumoto
* Category: syntax
* Target version: Next Major
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=begin
I'm very excited about this feature in CoffeeScript, and think it might be a nice-to-have thing in Ruby 2.0.

That's how I think it would look like:

 class Me
   def initialize(@name, @age, @location); end
 end

So we can declare ((|@variable|))s in the initializer method parameters definition to avoid assigning instance variables from method arguments by hand, like:

 class Me
   def initialize(name, age, location)
     @name = name
     @age = age
     @location = location
   end
 end

Want to hear what do you guys think, does that feature worth being included in 2.0?
=end



-- 
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