assigning to hash keys when there is a default value? - comp.lang.ruby

Message from discussion assigning to hash keys when there is a default value?

dbl...@wobblini.net

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More options Sep 2 2007, 10:19 pm

Newsgroups: comp.lang.ruby

From: dbl...@wobblini.net

Date: Mon, 3 Sep 2007 11:19:09 +0900

Local: Sun, Sep 2 2007 10:19 pm

Subject: Re: assigning to hash keys when there is a default value?

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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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