[ruby-core:84978] [Ruby trunk Feature#14336] Create new method String#symbol? and deprecate Symbol class

Issue #14336 has been updated by rosenfeld (Rodrigo Rosenfeld Rosas).


> it means that the developer doesn't think about his own application enough to know if something would be a String or Symbol, or uses user input without checking which is even worse

It has nothing to do with the developer but with the library author. They can't know whether the developer would want a symbol or a string as the hash key when deserializing back.

And this has nothing to do with user input, since the user doesn't talk directly to Redis.

> you should always check the documentation of the code you use to check all the corner cases where something would throw an Exception

Most of the time we spend coding is reading other's code. Most of the time other's code exist directly in the application and there's no documentation for them at all. You know, from the method name, that it's supposed to return a hash with identifier as keys, but you always have to check just to make sure those identifiers are strings or symbols, or maybe the hash is a HWIA. If Ruby was a static language, we would know immediately because the return value could be declared as Hash<String, Object> for example. But Ruby isn't, and it would be super helpful if whenever there's a hash with identifiers as keys we would know for sure that it must be strings, for example. Or, at least, that it doesn't matter whether we lookup by string or symbol.

There are lots of aging code bases around there and teams with high turnover rates. You can't just assume that all code in the code base was written by a single developer or a consistent team.

----------------------------------------
Feature #14336: Create new method String#symbol? and deprecate Symbol class
https://bugs.ruby-lang.org/issues/14336#change-69686

* Author: dsferreira (Daniel Ferreira)
* Status: Rejected
* 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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