Re: refactoring
Roedy Green wrote On 08/08/07 13:10,:
On Mon, 06 Aug 2007 20:19:06 GMT, Roedy Green
<see_website@mindprod.com.invalid> wrote, quoted or indirectly quoted
someone who said :
I have always felt that a if a method can have multiple inputs it
should be able to have multiple outputs, but very few language
designers (Forth and PostScript being exceptions) have agreed.
Places where multiple outputs would be useful:
Most of these seem better suited to using single
objects that wrap multiple values.
1. 2D and 3D co-ordinates, Cartesian to polar.
You'd ordinarily want the point or vector to be an
object in its own right, not something that had its
various components scattered in unrelated free-standing
variables.
2. returning a value with a status indicator about how good the value
is.
I imagine the status indicator would be something like
an error bar or a confidence interval. Again, it seems you
would want the indicator to accompany the "indicatee" rather
than floating around independently, and you'd achieve this
by putting both in a single object.
3. categorising routines. Using a separate method for each category
must repeat the binning logic.
I'm not sure what you mean by this.
4. division return quotient and remainder.
Here's a case where I agree: The hardware produces both
results, and it's a shame that we can't get them both in
one operation. (I can still recall being shocked to learn
that Java compilers would not optimize a paired /-and-% to
a single division, the way C and Fortran and so on have done
from time immemorial. It seems, in fact, that the JLS forbids
the optimization! Of course, the JIT can play fast and loose
with the JLS whenever it can tell it won't get caught.)
5. font/colour pair
The utility of multiple-valued expressions eludes me in
cases like this one. If it makes sense to keep the font and
the color (and the baseline angle/path, and the background
color, and ...) together, then it makes sense to create an
object to hold all these things. If it makes sense to treat
them separately, then why/how is one expression evaluating
both?
6. find min, max average of a set.
A SetStats object doesn't seem inconvenient to me.
If all we're doing is
double a;
long b;
char c;
(a,b,c) = method(x, y, z);
// use a, use b, use c
.... then I don't see a significant advantage over
Triplet t = method(x, y, z);
// use t.a, use t.b, use t.c
It seems to me that multiple-valued expressions (as opposed
to expressions yielding single objects that wrap multiple
values) aren't a whole lot of use unless there's a way to
do more with them than just pass them around. That quotient-
and-remainder thing, for instance: if the integer / operator
produced both, we'd need an expression syntax that could
plug both results into different parts of a formula. Go
too far along *that* path, and you'll come upon the smoking
ruins of APL ;-)
--
Eric.Sosman@sun.com