Re: Functions with package protection
Sorry to dig up this old post, but I still don't understand why 'package'
functions cannot be virtual? Is there a good reason for this? I can't see why
we can't use polymorphism on 'package' functions!
Is there way to make it virtual without making it public? (e.g. a 'virtual'
keyword?)
Thanks,
Simon TRENY
Jacob Carlborg Wrote:
In the D documentation at http://www.digitalmars.com/d/1.0/function.html
it says the following: All non-static non-private non-template member
functions are virtual, but this seems not to be the case. What I've
heard and as the following example shows functions declared as package
are non-virtual.
module main;
import tango.io.Stdout;
class A
{
package void foo ()
{
Stdout(A).newline;
}
}
class B : A
{
package void foo ()
{
Stdout(B).newline;
}
}
void main ()
{
A a = new B;
a.foo;
}
This will print A, but according to the documentation package is
virtual and therefore this should print B but doesn't. Either the
documentation is wrong or the compiler.
Compiled with GDC on OSX, I think it will give the same result with dmd
also.
Keeping a list of instances and garbage-collection
Hello,
I have a class A and I'd like to keep a list of all the created instances of
this class. To do that, I have a static List!(A) in the A class and, in the
constructor, I add each new instance to this list. This gives me the following
code:
class A {
private static List!(A) s_instances;
public this() {
s_instances.add(this);
}
public ~this() {
s_instances.remove(this);
}
public static void printAll() {
foreach (A instance; s_instances)
print(instance.toString());
}
}
But then, since all the instances are referenced by the static list, they are
never garbage-collected, which could be a problem. In some other languages,
this can be solved using weak references, but I haven't found any informations
about using weak references in D. Is there any way to solve this problem?
Thanks,
Simon
Returning a struct by reference
Hi there!
I'm quite new at D and I'm still just playing with it, but there is a thing
that I find currently missing. Sometimes, I'd like to be able to return a
struct by reference and not by value. For example, in the following example:
struct Position {
float x;
float y;
}
class Object {
private Position m_position;
public Position position() {
return m_position;
}
}
I'd like to be able to write things like this: myObject.position.x = 43 to
actually change the position of the object. But right now, since position is
a struct, it is returned by value and not by reference, and then the previous
instruction won't change the position of the object, but it will work on a copy
of the position field.
Here is the solutions that I can see to this problem:
- Returning a pointer to the position: public Position *position() { ... },
but I'd like to keep my code as free from pointers as possible.
- Make Position a class and not a struct. That could be a solution, but
then, when I'll do things like Position pos = object.position; pos.x = 43;,
it will effectively change the position of the object, which I wouldn't like
with this syntax.
Actually, I'd like to be able to do a thing like this:
public ref Position position() {
return m_position;
}
which would be the equivalent form to passing structs by reference in a
parameter.
Is there a way to do this in D?
Regards,
Simon
Re: Returning a struct by reference
grauzone Wrote:
Simon TRENY wrote:
Hi there!
I'm quite new at D and I'm still just playing with it, but there is a thing
that I find currently missing. Sometimes, I'd like to be able to return a
struct by reference and not by value. For example, in the following example:
struct Position {
float x;
float y;
}
class Object {
private Position m_position;
public Position position() {
return m_position;
}
}
I'd like to be able to write things like this: myObject.position.x = 43 to
actually change the position of the object. But right now, since position
is a struct, it is returned by value and not by reference, and then the
previous instruction won't change the position of the object, but it will
work on a copy of the position field.
Here is the solutions that I can see to this problem:
- Returning a pointer to the position: public Position *position() { ...
}, but I'd like to keep my code as free from pointers as possible.
- Make Position a class and not a struct. That could be a solution, but
then, when I'll do things like Position pos = object.position; pos.x =
43;, it will effectively change the position of the object, which I
wouldn't like with this syntax.
Actually, I'd like to be able to do a thing like this:
public ref Position position() {
return m_position;
}
which would be the equivalent form to passing structs by reference in a
parameter.
Is there a way to do this in D?
Yes. Make the variable public.
class Object {
Position position;
}
This code is even simpler than your's above. Incredible, isn't it?
Ok, but then, what if I'd like to make the variable read-only? i.e.
preventing the user from writing things like this:
myObject.position = pos2;
Regards,
Simon
Re: Returning a struct by reference
Daniel Keep Wrote:
Simon TRENY wrote:
Ok, but then, what if I'd like to make the variable read-only? i.e.
preventing the user from writing things like this:
myObject.position = pos2;
So... you're rejecting a solution on the basis that it prevents you from
doing the exact opposite of what you want to do?
*boggle*
-- Daniel
Here is a complete example of what I'd like to achieve:
struct Position {
private float m_x;
private float m_y;
public float x() {
return m_x;
}
public void x(float x) {
m_x = x;
EmitSignal(changed);
}
public float y() {
return m_y;
}
public void y(float y) {
m_y = y;
EmitSignal(changed);
}
}
class Object {
private Position m_position;
public this() {
m_position.CallOnSignal(changed, onPositionChanged);
}
//This syntax is not working
public ref Position position() {
return m_position;
}
public void onPositionChanged() {
writeln(Position Changed!!);
}
}
With this fictional code, I could write things like:
object.position.x = 14; and the object will be aware that its position has
changed.
Making the position-variable public will lead the user to be able to do
things like this:
object.position = pos2; and then, the object won't be aware that its position
has changed. And this is a problem for me.
I hope it's clearer now
Re: Returning a struct by reference
grauzone Wrote:
Simon TRENY wrote:
grauzone Wrote:
Simon TRENY wrote:
Hi there!
I'm quite new at D and I'm still just playing with it, but there is a
thing that I find currently missing. Sometimes, I'd like to be able to
return a struct by reference and not by value. For example, in the
following example:
struct Position {
float x;
float y;
}
class Object {
private Position m_position;
public Position position() {
return m_position;
}
}
I'd like to be able to write things like this: myObject.position.x = 43
to actually change the position of the object. But right now, since
position is a struct, it is returned by value and not by reference, and
then the previous instruction won't change the position of the object,
but it will work on a copy of the position field.
Here is the solutions that I can see to this problem:
- Returning a pointer to the position: public Position *position() { ...
}, but I'd like to keep my code as free from pointers as possible.
- Make Position a class and not a struct. That could be a solution,
but then, when I'll do things like Position pos = object.position; pos.x
= 43;, it will effectively change the position of the object, which I
wouldn't like with this syntax.
Actually, I'd like to be able to do a thing like this:
public ref Position position() {
return m_position;
}
which would be the equivalent form to passing structs by reference in a
parameter.
Is there a way to do this in D?
Yes. Make the variable public.
class Object {
Position position;
}
This code is even simpler than your's above. Incredible, isn't it?
Ok, but then, what if I'd like to make the variable read-only? i.e.
preventing the user from writing things like this:
myObject.position = pos2;
Then you write a getter that simply returns the field by value.
The D compiler will (hopefully) inline the getter function, so there
shouldn't be a disadvantage in performance.
If I add a getter-property that returns the field by value, the following
instruction object.position.x = 12; won't modify the position of the object,
but will only modify the returned copy of the position, right?
That's actually why I'd like to have a getter that returns the field by
reference and not by value.
Note: I think D2.0 wants to introduce ref-returns at some point in the
future.
Regards,
Simon
