From: danieldasilvaferreira@...
Date: 2018-01-08T17:47:19+00:00
Subject: [ruby-core:84731] [Ruby trunk Feature#14336] Create new method String#symbol? and deprecate Symbol class

Issue #14336 has been updated by dsferreira (Daniel Ferreira).


> It sounds like these would still be broken, with no deprecation warning:

> h['a'] = 1
> h[:a] = 2
> h['a'] # was 1, now 2

> 'a' == :a # was false, now true

> 'a'.hash == :a.hash # was false, now true
> I don't see any transition plan for the C-API.

From my proposal:

bar = :foo
bar.class # => String
bar.symbol? # => true

baz = "foo"
baz.class # => String
baz.symbol? # => false

bar == baz # => false

h[bar] == h[baz] # => ? Open to discussion but I would discuss it in a different issue. Not this one. For now lets not break backwards compatibility.

Lets keep current C API in the background.  (Since we still have performance gains by using symbols in certain situations maybe we can use the mechanism in some degree and do the optimisations in the brackground (Not sure if this is feasible or not!))

----------------------------------------
Feature #14336: Create new method String#symbol? and deprecate Symbol class
https://bugs.ruby-lang.org/issues/14336#change-69451

* Author: dsferreira (Daniel Ferreira)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
From  the discussions on the three previous issues related to the String vs Symbol subject ([5964](https://bugs.ruby-lang.org/issues/5964), [7792](https://bugs.ruby-lang.org/issues/7792), [14277](https://bugs.ruby-lang.org/issues/14277)) there are some conclusions we can assume:
* Current String vs Symbol is not the ideal scenario. See: Matz and Koichi comments.
* Current philosophy is to use Symbols as identifiers and Strings when strings are needed.
* Current situation is that Symbols are being used in many code bases as strings except for strings that really need the String methods.
* Current situation is that we are designing APIs to handle both String and Symbol inputs forcing an overhead of API development.

I propose the deprecation of `Symbol` class and the introduction of `String#symbol?`.

```ruby
foo = :foo
foo.class # => String
foo.symbol? # => true
bar = "bar"
bar.class # => String
bar.symbol? # => false
```

For backwards compatibility transition path I propose:

```ruby
class Symbol
  def self.===(var)
    warn ("Warning message regarding deprecated class")
    if var.class == Symbol
      true
    elsif var.class == String && var.symbol?
      true
    else
      false
    end
  end
end

class String
  def is_a?(klass)
    case klass
    when String
      true
    when Symbol
      self.symbol?
    else
      false
    end
  end
end
```



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