From: danieldasilvaferreira@...
Date: 2018-01-08T15:36:16+00:00
Subject: [ruby-core:84724] [Ruby trunk Bug#14336] Create new method String#symbol? and deprecate Symbol class

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


There is also one important thing here that deserves consideration: We are doing a great effort to improve the performance of strings and everything associated to them.

Symbols are not taking advantage of those improvements.

If we keep saying that everything is a Symbol except user input we will be constraining ourselves to use less performant code. Correct me if I���m wrong but if I���m not mistaken immutable strings can be more performant then symbols, not to mention the memory consumption. 

By merging symbols into strings we can focus all our efforts in improving string���s performance leaving symbols out of the equation.

I only see positive things here.

The transition path that I present will make sure that no code will be broken.




----------------------------------------
Bug #14336: Create new method String#symbol? and deprecate Symbol class
https://bugs.ruby-lang.org/issues/14336#change-69444

* Author: dsferreira (Daniel Ferreira)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
----------------------------------------
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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