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Date: Sun, 24 Jul 2011 09:16:08 -0700
From: Patricia Shanahan <pats@acm.org>
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Subject: Re: Arithmetic overflow checking
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On 7/23/2011 7:55 PM, Henderson wrote:
> On 23/07/2011 5:03 PM, Andreas Leitgeb wrote:
>> It is my opinion, that operator overloading at least for a certain
>> limited set of JSL classes (including BigDecimal and BigInteger as
>> well as some new Complex class in addition to String's +), would
>> be beneficial. Ditto for a new "strictint" keyword to enable
>> detection and handling of integer overflows.
>
> An obvious suggestion would be to allow it on all java.lang.Number
> subclasses, but a + b among these is only defined if a is a Number class
> that has an overload of .plus(x) that is applicable to an argument of a
> supertype of b, and the most specific such is chosen; and if a is a
> primitive, is treated as b + a; a * b analogously; a - b with a
> primitive uses (b - a).negate() and expects the return type of minus to
> support negate(); and for division we likewise need .reciprocal().
>
> We could go further and rewrite Number.java so that it is Number<T
> extends Number<T>> and defines:

I don't think it would be wise to tie operator overloading to Number.
Number defines a series of conversions that make some sense for those
types that represent subsets of the real line.

You cannot return "the value of the specified number as a double" if the
specified number is complex. I would prefer the complex type to have
separate, meaningfully named, methods returning as double each of the
real part, the complex part, the absolute value, and the phase.

I think it might be better to create a marker interface
java.math.Arithmetic. I do like the idea of a fixed mapping from
operators to method names that are normal identifiers. I don't think
all arithmetic types should be required to support all operations. For
example, consider negate and an unsigned type, or reciprocal and an
integer type.

Patricia