PRE-RFC: Add getters and setters for global variables

[sampersand]

This is quite niche, so it's probably not super important but...

Global variables in Ruby have "getters" and "setters". For user-defined global variables, the type of the global is the same when both getting and setting. However, quite a few builtin globals ($., $-F, $0, etc.) can be assigned more permissive types, and convert them. (For example, $. can be assigned ints, but converts them internally.)

I propose "global variable setter and getter" syntax:

$.: Integer
$.:= int

$0: String 
$0:= string

$-F: String | Regexp | nil
$-F:= string | Regexp | nil

If no setter is supplied, the global variable is assumed to have both the same getter and setter.

[ParadoxV5]

should be

$.: Integer
$.=: int

$0: String 
$0=: string

$-F: String | Regexp | nil
$-F=: string | Regexp | nil

to match def attribute=: …

[sampersand]

That could work, but what about $=? $== feels a bit weird like it could be an actual variable

[ParadoxV5]

$ isn’t a global variable is it… (;
$== … will this become a global variable itself…