From: dblack@...
Date: 2007-09-03T11:19:09+09:00
Subject: Re: assigning to hash keys when there is a default value?

Hi --

On Mon, 3 Sep 2007, 7stud -- wrote:

> Can someone explain why there is a difference in the second line of
> output for the two hashes:
>
> h = Hash.new(5)
>
> puts h[2]
>
> h[2] ||= 10
> p h
>
> #----------
> puts
> #----------
>
> h = Hash.new
>
> puts h[2]
>
> h[2] ||= 10
> p h
>
> ---output:--
> 5
> {}
>
> nil
> {2=>10}

x ||= y is, I think, always supposed to be exactly equivalent to
x = x || y, so that line in your first hash should be equivalent to:

   h[2] = 5 || 10

which should assign 5 to h[2]. It looks to me like you've found a bug.
I can't think of any reason (and I really hope there isn't one,
because having an exception to that ||= rule would be very messy) why
using a default hash value would make any difference here. It's still
5 || 10 on the rhs, and it's still just an assignment.


David

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