overloaded casting question

[laniik]

Hi. Im just wondering what the syntax to overload a casting operator
is. For example, i have

struct Point {
float x,y,z;
};

struct Vector {
float a,b,c;
};

and i want to be able to do somthing like

Point p;
Vector v;

((Point)v).x++;

thanks

[Victor Bazarov]

laniik wrote:

Hi. Im just wondering what the syntax to overload a casting operator
is. For example, i have

struct Point {
float x,y,z;
};

struct Vector {
float a,b,c;
};

and i want to be able to do somthing like

Point p;
Vector v;

((Point)v).x++;

I would strongly advise against it. What you really want is to create
an interface to treat the Vector's elements as if they had names x, y, or
z. You can introduce member functions for that.

struct Vector {
float a,b,c;
float& x() { return a; }
};

Now write

v.x()++;

V

[Victor Bazarov]

Victor Bazarov wrote:

laniik wrote:

Hi. Im just wondering what the syntax to overload a casting operator
is. For example, i have

struct Point {
float x,y,z;
};

struct Vector {
float a,b,c;
};

and i want to be able to do somthing like

Point p;
Vector v;

((Point)v).x++;

I would strongly advise against it. What you really want is to create
an interface to treat the Vector's elements as if they had names x, y, or
z. You can introduce member functions for that.

struct Vector {
float a,b,c;
float& x() { return a; }
};

Now write

v.x()++;

V

Another way is to derive Vector from Point, of course.

V

[Artie Gold]

Victor Bazarov wrote:

Victor Bazarov wrote:

laniik wrote:

Hi. Im just wondering what the syntax to overload a casting operator
is. For example, i have

struct Point {
float x,y,z;
};

struct Vector {
float a,b,c;
};

and i want to be able to do somthing like

Point p;
Vector v;

((Point)v).x++;

I would strongly advise against it. What you really want is to create
an interface to treat the Vector's elements as if they had names x, y, or
z. You can introduce member functions for that.

struct Vector {
float a,b,c;
float& x() { return a; }
};

Now write

v.x()++;

V

Another way is to derive Vector from Point, of course.

V

<ack> <gag> <splutter>

Is a Vector a Point?

</ack> </gag> </splutter>
;-)

--ag
--
Artie Gold -- Austin, Texas
http://it-matters.blogspot.com (new post 12/5)
http://www.cafepress.com/goldsays

[laniik]

hm. just out of curosity, why do you advise against it. Really, the
reason is not so i can rename the variables, that was just an example
of what they do. The reason i would want to do that is because i often
find myself wanting to perform vector functions on points:

example.

Vector v;
Point p;

v.a=p.x;
v.b=p.y;
v.c=p.z;

Vector::normali ze(v);

where really i would like to remove the need of those 3 lines, and have

Vector::normali ze((Vector)p);

for example.

thanks
oliver

[laniik]

a vector is not a point, of course, but they are similar in terms of
local data, and im often wanting to perform vector operations on a
vector that woul have the same values as a specific point.

[laniik]

also,

(regardless of the correctness of vectors/points) im also curious how
its done!

: )

[lilburne]

Victor Bazarov wrote:

Now write

v.x()++;

V

Another way is to derive Vector from Point, of course.

I don't think our mathematicians would agree, in fact I can
point to 10 years of interminable arguments about a point
isn't a vector, etc, etc.

class Point {
public:

double x();
double y();
double z();
Vector release();
};

class Vector {
public:

double i();
double j();
double k();
Point anchor();
};

[Victor Bazarov]

laniik wrote:

hm. just out of curosity, why do you advise against it.
You're trying to introduce a tight coupling where none seem to exist.
If you know that it does in fact exist, there are better ways to put it
into C++ terms. See Inheritance, Containment, Implementation in terms of
and so on...
Really, the
reason is not so i can rename the variables, that was just an example
of what they do. The reason i would want to do that is because i often
find myself wanting to perform vector functions on points:

example.

Vector v;
Point p;

v.a=p.x;
v.b=p.y;
v.c=p.z;

Vector::normali ze(v);

where really i would like to remove the need of those 3 lines, and have

Vector::normali ze((Vector)p);

for example.

What does it mean to normalize a point if that point is not a vector?
What you need, probably is a way to convert one into the other. Define
respective parameterized constructors in each class.

class Point;

struct Vector {
float a,b,c;
Vector(Point const &p);
};

struct Point {
float x,y,z;
Point(Vector const &v);
};

Vector::Vector( Point const &p) : a(p.x), b(p.y), c(p.z) {}
Point::Point(Ve ctor const &v) : x(v.a), y(v.b), z(v.c) {}
V

[lilburne]

laniik wrote:

hm. just out of curosity, why do you advise against it. Really, the
reason is not so i can rename the variables, that was just an example
of what they do. The reason i would want to do that is because i often
find myself wanting to perform vector functions on points:

example.

Vector v;
Point p;

v.a=p.x;
v.b=p.y;
v.c=p.z;

Vector::normali ze(v);

where really i would like to remove the need of those 3 lines, and have

Vector::normali ze((Vector)p);

for example.

Points and vectors are our stock in trade. Most of the time
we don't have any real problems with keeping them seperate
and converting a Point to a Vector and back again as needed,
besides our vector class has a cached length too. Heck we
even have a UnitVector class too. For us the important thing
is clarity in the code, and a minimal use of casting. If we
really need to get jiggywithit these things get converted to
raw arrays.