From: Colin Bartlett <colinb2r@...>
Date: 2010-01-24T13:03:08+09:00
Subject: Re: how to define []=

On Sat, Jan 23, 2010 at 4:56 PM, Marnen Laibow-Koser wrote:
> Second, it's a bad idea: to experienced Ruby programmers,
> [i, j] is slicing, not subscripting.  Just use the standard [i][j].

You're right to observe that it's likely to be confused with slice,
a point which had escaped me when I made my post:
  arr = [0, 1, 2, 3, 4]  #=> [0, 1, 2, 3, 4]
  arr[1, 3] = 7          #=> 7
  arr                    #=> [0, 7, 4]
So, yes, the sort of thing in my post should almost always be avoided.

That said, there may be occasions when it might be useful,
suitably documented of course!

> First of all, I don't think that will work.

Well, things like that worked a year or so ago,
when I was looking closely into how Ruby assignment
worked with []= methods, and they still seem to work!
I think the following shows how Ruby deals with
a mix of arguments on the LHS and RHS
of an assignment method which uses []=

  class QQ
    def []=( *args )
      puts "#args== " + args.inspect
      # you can put some complicated code here
      # which relies on the structure of args
    end
  end
  q = QQ.new  #=> #<QQ:0x2746040>

  q[]        = 100  #args== [100]          #=> 100
  q[0]       = 100  #args== [0, 100]       #=> 100
  q[0, 1]    = 100  #args== [0, 1, 100]    #=> 100
  q[0, 1, 2] = 100  #args== [0, 1, 2, 100] #=> 100

  q[]        = 100, 101  #args== [[100, 101]]          #=> [100, 101]
  q[0]       = 100, 101  #args== [0, [100, 101]]       #=> [100, 101]
  q[0, 1]    = 100, 101  #args== [0, 1, [100, 101]]    #=> [100, 101]
  q[0, 1, 2] = 100, 101  #args== [0, 1, 2, [100, 101]] #=> [100, 101]

You can even do things like:
  q[0, [10, 11], 2] = 100, 101  #args== [0, [10, 11], 2, [100, 101]]
                                #=> [100, 101]

But I'll end by repeating my endorsement of your admonishment!