A way to implement `String#split!`

Question

Sometimes I need such method, which could change class of its own object. There are String#delete!, #downcase!, #encode!, #gsub!, #strip!, #slice!, etc. They are all trying to change string, but resulting class is anyway still String. And I want a method, which can convert String to Array. Some way to make this:

irb(main):082:0> str = "qwerty"
=> "qwerty"
irb(main):083:0> str.split! "e"
=> ["qw", "rty"]
irb(main):084:0> str
=> ["qw", "rty"]

Is it possible? Maybe some cool japan kung-fu or ugly bicycles — I would like to see any solution.

Answer 1

Nope, not possible. Objects can't change their classes in Ruby.

In Smalltalk, for example, you could use become::

becomeSubStrings: aString
    self become: (self subStrings: aString).

If you call it like this:

s := 'qwerty'.
s becomeSubStrings: 'e'.

Now, s is an array:

Transcript show: s printString.

The result is:

#('qw' 'rty')

Technically, become: doesn't change the class of the object, rather it lets one object become another object. In this case, we let self become the result of self subStrings:, which splits the string into an array of substrings. The result is the same: the original string receiver is now an array.

Answer 2

Jörg W Mittag's answer is solid. It is a fundamental attribute of Ruby as a language that you can't change an object's class.

The best you can do is re-assign the variable as I am sure you are already doing:

irb(main):082:0> str = "qwerty"
=> "qwerty"
irb(main):083:0> str = str.split "e"
=> ["qw", "rty"]
irb(main):084:0> str
=> ["qw", "rty"]

Answer 3

This is only possible using evil-ruby (at least I'm pretty sure evil-ruby supports this). It is a really clever hack that coaxes Ruby into doing things it was never meant to do, but also an unportable hack that has been known to cause actual segfaults in Ruby code using it. You should absolutely not use it in production code.

Otherwise, give your string an internal array and make it delegate all messages to the array (along the lines of BlankSlate + Forwardable).

It's still not something I would want to do. I can't imagine a situation where such a minor convenience outweighs the hackness of the implementation.