[110] in java-interest
multiple return values
daemon@ATHENA.MIT.EDU (Jerry Morrison)
Mon May 22 20:28:21 1995
Date: 22 May 1995 17:20:25 -0800
From: "Jerry Morrison" <jerry.morrison@3do.com>
To: "java-interest <java-interest@java.sun.com>" <java-interest@java.sun.com>
The Java language team asked how Mesa procedures return multiple values.
In short, return a "struct" and use "constructors" and "extractors" to make
it convenient. I'll express this in a C-like syntax but I'm not sure whether
to use () or {} for constructors and extractors. Mesa syntax is more regular
and more readable.
typedef struct Point { int x; int y; } Point;
Point point;
int i, width, height;
point = {10, 2}; /* constructor */
{width, height} = point; /* extractor assigns to width and height in
parallel */
A one-element struct auto-coerces to its element type, but not vice versa.
typedef struct Prime { int i; } Prime;
Prime prime = {13}; /* constructor */
i = prime; /* auto-coercion */
{i} = prime; /* extractor */
i = prime.i; /* explicit field selection */
A procedure returns multiple values via constructor
... return {cos(angle), sin(angle)};
and the caller gets all the results via extractor
{x, y} = PolarToRectangular(radius, angle);
In Mesa, every procedure's bundle of arguments is an anonymous struct type,
and calling it involves a constructor. Every procedure returns an anonymous
struct type, and getting the results involves an extractor or auto-coercion
to one element. Mesa also has constructors and extractors that refer to
elements by name instead of position.
Hope this helps.
Jerry
-
Note to Sun employees: this is an EXTERNAL mailing list!
Info: send 'help' to java-interest-request@java.sun.com
