Why doesn't Ruby support i++ or i--​ (increment/decrement operators)?

Question

The pre/post increment/decrement operator (++ and --) are pretty standard programing language syntax (for procedural and object-oriented languages, at least).

Why doesn't Ruby support them? I understand you could accomplish the same thing with += and -=, but it just seems oddly arbitrary to exclude something like that, especially since it's so concise and conventional.

Example:

i = 0    #=> 0
i += 1   #=> 1
i        #=> 1
i++      #=> expect 2, but as far as I can tell, 
         #=> irb ignores the second + and waits for a second number to add to i

I understand Fixnum is immutable, but if += can just instanciate a new Fixnum and set it, why not do the same for ++?

Is consistency in assignments containing the = character the only reason for this, or am I missing something?

Answer 1

Here is how Matz(Yukihiro Matsumoto) explains it in an old thread:

Hi,

In message "[ruby-talk:02706] X++?"
    on 00/05/10, Aleksi Niemelä <[email protected]> writes:

|I got an idea from http://www.pragprog.com:8080/rubyfaq/rubyfaq-5.html#ss5.3
|and thought to try. I didn't manage to make "auto(in|de)crement" working so
|could somebody help here? Does this contain some errors or is the idea
|wrong?

  (1) ++ and -- are NOT reserved operator in Ruby.

  (2) C's increment/decrement operators are in fact hidden assignment.
      They affect variables, not objects.  You cannot accomplish
      assignment via method.  Ruby uses +=/-= operator instead.

  (3) self cannot be a target of assignment.  In addition, altering
      the value of integer 1 might cause severe confusion throughout
      the program.

                            matz.