From: dblack@...
Date: 2007-09-03T21:29:55+09:00
Subject: Re: assigning to hash keys when there is a default value?

Hi --

On Mon, 3 Sep 2007, Russell Norris wrote:

> I don't think this is a bug, kittens. since h[2] returns a value [even
> though it's not set], it causes h[2] to evaluate so the assignment
> never happens. x ||= y just means give me x or set x to y if there's
> no value for x. h[2] _does_ have a value if only a default one.
>
> just my two cents.
>
> unless i missed the point here, in which case i apologize for my hasty
> conclusion. :))

The thing is, this:

   x ||= y

always means (at least, so I've always been told):

   x = x || y

which in the case of the hash with a default value of 5, would mean:

   h[2] = 5 || 10

In other words: h.[]=(2, 5||10)

At that point, the default value is out of the picture. The default
value has no implications for the #[]= (writer) method; it's only what
you get when you use the #[] (reader) method.

So what's at stake here is the matter of x ||= y behaving predictably.
I have to say, it's a case where I'm not even really concerned with
the implementation (e.g., whether it uses [] on its way to []=) but
just the semantics. I don't like the idea that the syntactic sugar is
actually not a reliable drop-in replacement for the thing it's
sugaring.


David

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