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Re: Java puzzler

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On 05/11/2011 04:57 PM, Tom Anderson wrote:
> 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.

Well, if you step back and look at it from the semantic point of view, 
what the compiler sees at both instances the following pattern:
<variable of type byte> += <expression of type int>. You could redefine 
literals of smaller numeric type, which makes the expression computation 
rules confusing (is (1001 - 1000) a byte, short, or int?). However, as 
long as byte, short, and char promote to int for integer computation, it 
still doesn't solve the += problem. You could change them to not promote 
to int, but that starts to cause interesting tangles in Java (the VM 
would either need to have instructions for all arithmetic instructions 
in byte, short, and char counterparts, in addition to the int, float, 
long, and double counterparts, or it would have to emit narrowing 
conversions after every subcomputation in an expression).

But I can see reasons to allow your `b += i' expressions. Consider that 
use of the byte and short types are relatively rare, as they are only 
effective in memory reduction when used in arrays [1]. It is not 
unimaginable that many constants have type int but are naturally 
applicable to byte or short values. In such a case, b += i would make sense.

> So, would it have been possible to write the language rules such that
> integer literals have either some sort of indeterminate-length
> pseudo-type that can be used submissively in all sorts of expressions,
> or to have small integer literals have type byte, bigger ones type
> short, and so on?

Yes, it would have been possible, but if you throw in the results of 
compile-time constant expressions, things might get ugly. It also makes 
computing the type of a literal somewhat uglier for rather little benefit.

[1] Well, the JVM could theoretically pack bytes, shorts, and chars 
inside classes, but I'm not sure if this is done in practice.

-- 
Beware of bugs in the above code; I have only proved it correct, not 
tried it. -- Donald E. Knuth

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Re: Java puzzler Gábor Bakos <aborgabor@gmail.com> - 2011-05-11 01:44 -0700
  Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-11 05:24 -0700
    Re: Java puzzler Tom Anderson <twic@urchin.earth.li> - 2011-05-11 21:57 +0100
      Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-11 16:07 -0700
        Re: Java puzzler Tom Anderson <twic@urchin.earth.li> - 2011-05-12 21:38 +0100
          Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-12 13:45 -0700
            Re: Java puzzler Nancy 3 <n3@gmai1.c0m> - 2011-05-12 16:56 -0400
              Re: Java puzzler markspace <-@.> - 2011-05-12 14:32 -0700
                Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-12 16:05 -0700
                Re: Java puzzler markspace <-@.> - 2011-05-12 17:40 -0700
                Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-12 18:18 -0700
                Re: Java puzzler markspace <-@.> - 2011-05-12 19:26 -0700
                Re: Java puzzler Tom Anderson <twic@urchin.earth.li> - 2011-05-14 10:18 +0100
                Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-14 08:09 -0700
                Re: Java puzzler Lew <noone@lewscanon.com> - 2011-05-14 13:00 -0400
                Re: Java puzzler Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-05-14 15:08 -0400
                Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-14 13:25 -0700
                Re: Java puzzler markspace <-@.> - 2011-05-14 08:46 -0700
                Re: Java puzzler Spock <spock@starfleet.ufp> - 2011-05-14 19:33 -0400
                Re: Java puzzler Tom Anderson <twic@urchin.earth.li> - 2011-05-15 00:41 +0100
                Re: Java puzzler markspace <-@.> - 2011-05-14 18:35 -0700
                Re: Java puzzler Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-05-14 23:43 -0400
                Re: Java puzzler Tom Anderson <twic@urchin.earth.li> - 2011-05-15 11:16 +0100
                Re: Java puzzler markspace <-@.> - 2011-05-15 05:40 -0700
                Re: Java puzzler Tom Anderson <twic@urchin.earth.li> - 2011-05-15 15:23 +0100
                Re: Java puzzler markspace <-@.> - 2011-05-15 08:09 -0700
                Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-15 07:37 -0700
                Re: Java puzzler markspace <-@.> - 2011-05-15 08:00 -0700
                Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-15 08:16 -0700
                Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-15 07:35 -0700
                Re: Java puzzler markspace <-@.> - 2011-05-15 08:11 -0700
                Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-15 08:15 -0700
                Re: Java puzzler Lew <noone@lewscanon.com> - 2011-05-15 13:11 -0400
                Re: Java puzzler Nancy 3 <n3@gmai1.c0m> - 2011-05-12 20:47 -0400
                Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-12 18:00 -0700
                Re: Java puzzler markspace <-@.> - 2011-05-12 18:01 -0700
                Re: Java puzzler Nancy 3 <n3@gmai1.c0m> - 2011-05-12 21:22 -0400
                Re: Java puzzler Patricia Shanahan <pats@acm.org> - 2011-05-12 18:32 -0700
                Re: Java puzzler Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-12 22:34 -0400
              Re: Java puzzler Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-12 22:27 -0400
      Re: Java puzzler "John B. Matthews" <nospam@nospam.invalid> - 2011-05-12 00:28 -0400
      Re: Java puzzler Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-05-12 10:33 -0400
  Re: Java puzzler Lew <noone@lewscanon.com> - 2011-05-11 09:12 -0400
  Re: Java puzzler Lew <noone@lewscanon.com> - 2011-05-11 09:13 -0400
  Re: Java puzzler markspace <-@.> - 2011-05-11 08:00 -0700

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