From: Robert Klemme <shortcutter@...>
Date: 2007-09-05T18:49:14+09:00
Subject: Re: assigning to hash keys when there is a default value?

2007/9/5, Pe�a, Botp <botp@delmonte-phil.com>:
> From: Robert Klemme [mailto:shortcutter@googlemail.com]
> # 2007/9/4, Yossef Mendelssohn <ymendel@pobox.com>:
> # > If '"x+=1" will always be "x=x+1"', what's the problem in
> # having x ||=
> # > 1 always be x = x || 1?
> # That an assignment of x=x is useless (basically a nop in the standard
> # case of x being a variable).
>
> consider,
>
> irb(main):074:0* h=Hash.new
> => {}
> irb(main):075:0> h[5] = h[5]
> => nil
> irb(main):076:0> h
> => {5=>nil}
> irb(main):062:0* h=Hash.new(1)
> => {}
> irb(main):063:0> h[5] = h[5]
> => 1
> irb(main):064:0> h
> => {5=>1}
>
> thus h[k] = h[k] could mean
>     h[k] = h.default   or
>     h[k] = nil
>
> definitely not useless and not noop.

I said "noop in the standard case of a variable".  We can certainly
debate about usefulness or uselessness.  I concede that it's not free
of side effects in the case of a Hash, but the only noticeable side
effect is the change of the key set.  Assigning with the Hash's
default is not visible through Hash#[] although it is with #fetch
which seems to be rarely used from what I see.  So I still say that
usefulness of self assignment is very limited.

Kind regards

robert