Remove deprecated methods

[patricklinpl]

Part of #3039

Remove deprecated methods:

• Dir.exists?
• File.exists?
• Kernel#=~

[patricklinpl]

i thought using nil here would make sense since =~ returns nil; would it be better to just return true?

[nirvdrum]

=~ returned nil as the default implementation. But, if a class defines =~ then !~ will call that version. You can see the dynamic call in CRuby:

https://github.com/ruby/ruby/blob/7b93e65e9f9cb7abfc7e19aff4da9d6e4c32de4b/object.c#L1629-L1634

As an example:

class X
  def =~(other)
    puts :hi
  end
end

X.new !~ "abc"

That will print out 'hi' because !~ delegates to =~.

[patricklinpl]

ohh i see thanks; i used respond_to to check for an implantation, is there a better approach?

[eregon]

@andrykonchin already has a PR for this in #3444, he will try to rebase his PR on top of this one.