Re: operator overloading

From:
Patricia Shanahan <pats@acm.org>
Newsgroups:
comp.lang.java.programmer
Date:
Tue, 27 May 2008 10:58:18 -0700
Message-ID:
<g1hi3s$t7t$2@ihnp4.ucsd.edu>
Tom Anderson wrote:

On Tue, 27 May 2008, Patricia Shanahan wrote:

Tom Anderson wrote:

On Mon, 26 May 2008, Patricia Shanahan wrote:

Wojtek wrote:

Arne VajhHj wrote :

Operators only make the code more readable for classic arithmetic.


Which is my point.


Maybe this subthread suggests a solution. Define, for example, an
interface Addable<T> with

T additionOperation(T o);

as its only method.


Analogising to multiplication, this is going to make it impossible to
write my Matrix class which can be multiplied any of a double, a
Vector, or another Matrix, because you can't implement multiple
instances of a generic interface. Well, you could, but you'd have to
do an instanceof switch inside additionOperation, or implement some
kind of ugly bounce dispatch.

Anyway, i'm not happy with this solution, although i appreciate and
strongly agree with its intent.


Good point. How about this modification?

Addable, Multipliable, etc. become marker interfaces. Suppose a is a
reference to Multipliable or a type implementing Multipliable. Then
the compiler would process a+b as though it were
a.multiplicationOperation(b).


I'm happy with this. What you describe is exactly how it works in python
or C++, with a slightly different method name, and requiring a marker
interface. Could we even drop the marker interface? What do we gain by
having it?

....

The marker interface avoids any backwards compatibility problems with a
method called "additionOperation" that is not intended to be used to
implement "+".

Patricia

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