Struct "inheritance"

Vidar Wahlberg canidae at exent.net
Sat Feb 4 04:55:55 PST 2012


On 2012-02-04 13:06, Simen Kjærås wrote:
> It seems that what you want is alias this:

Thank you both, that's exactly what I needed.

Leeching a bit more on the thread:
Going back to the method:
int somethingNifty(Point p) {
   return p.x + p.y;
}

Let's say I have the following code:
for (x; 0 .. 10) {
   for (y; 0 .. 10) {
     Point p = {x, y};
     somethingNifty(p);
   }
}

[How] can you rewrite those two statements inside the loops to a single 
line? For example (this doesn't work):
somethingNifty(Point(x, y));


And finally a question about operator overloading, here's the code for 
"Coordinate" ("Point" is similar in structure):
import Point;
struct Coordinate {
   Point _point;
   int _z;
   @property auto point() const {
     return _point;
   }
   @property auto point(Point point) {
     return _point = point;
   }
   @property auto z() const {
     return _z;
   }
   @property auto z(int z) {
     return _z = z;
   }
   bool opEquals(ref const Coordinate c) const {
     return z == c.z && point == c.point;
   }
}

Compilation fails with the following error:
Coordinate.d:18: Error: function Point.Point.opEquals (ref const 
const(Point) p) const is not callable using argument types 
(const(Point)) const
Coordinate.d:18: Error: c.point() is not an lvalue

Noteworthy the code compiles fine if i replace "point" and "c.point" 
with "_point" and "c._point", but then I'm referencing _point directly 
instead of through the property "point" (which may do something else 
than just return _point in the future).
I've looked at 
http://www.d-programming-language.org/operatoroverloading.html#equals 
and that page is slightly confusing. It claims that:
If structs declare an opEquals member function, it should follow the 
following form:
struct S {
   int opEquals(ref const S s) { ... }
}

However, I can't even get the code to compile if I do that, the compiler 
(gdc-4.6) says:
Error: function Coordinate.Coordinate.opEquals type signature should be 
const bool(ref const(Coordinate)) not int(ref const const(Coordinate) c)


I hope it's somewhat clear what I'm trying to achieve.


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