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NNTP-Posting-Date: Wed, 11 May 2011 18:07:38 -0500
Date: Wed, 11 May 2011 16:07:37 -0700
From: Patricia Shanahan <pats@acm.org>
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Subject: Re: Java puzzler
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On 5/11/2011 1:57 PM, Tom Anderson wrote:
> On Wed, 11 May 2011, Patricia Shanahan wrote:
...
>> Without the implicit cast to the left hand side type, "+=" could not
>> have been used for byte, char, or short. The arithmetic operation
>> promotes to int, and there would be no way to cast back to the target
>> type.
>
> Well, that's true if one takes as given that the operation promotes to
> int. Could it have been specified not to?

Sure, but that would create other weirdness. For example:

byte b = 100;
byte c = 100;
int i = b + c;

would assign -56 to i, because that is the byte result of the addition.

>
> If we're talking about things like:
>
> byte b = 0;
> b += 2;
>
> The i agree that that should compile - it would be agonizing if it
> didn't. But i see no earthly reason why this:
>
> byte b = 0;
> int i = 1000000;
> b += i;
>
> Should compile. Where you're using a literal, you have no way to make
> the literal one size of integer or another, but when you're using a
> variable, you do; an offset for a byte can be a byte itself.

I don't understand this argument, because (byte)2 is a constant
expression of type byte. I think the core issue is the use of int for
results of narrow integer arithmetic.

Patricia