Re: delegate !is null
On Tue, 08 Sep 2009 18:13:56 -0400, Saaa em...@needmail.com wrote:
Hope this one makes any sense :)
C c = new C;
C mouseOverObject = c;
int delegate() deleg = mouseOverObject.getSomeVariable;
mouseOverObject = null;
int value;
void write()
{
if(deleg !is null) //how do I make this check for (mouseOverObject !is
null)?
if(mouseOverObject !is null)
That's the only way. A delegate does not magically become set to null
when you set the original object to null or delete the original object.
It is a separate pointer that is only set when you set it.
What you are asking is the equivalent of this:
int x = 5;
int y = x;
x = 0;
if(y != 0) // how do I check through y that x is now 0?
However, setting mouseOverObject to null does *not* destroy the object, as
long as the delegate exists, it is still pointing to the object, so it
will not be cleaned by the GC.
So your delegate is still valid as long as you don't delete
mouseOverObject manually.
-Steve
Re: delegate !is null
Steven Schveighoffer schvei...@yahoo.com wrote in message news:op.uzxs4wyreav...@localhost.localdomain... On Sun, 06 Sep 2009 18:54:47 -0400, Saaa em...@needmail.com wrote: I'd like to set D's delegate to a method which is not yet available (like c.method). I solved this by encapsulating the method within a function literal, but I also need to know whether the method is available or not when calling the delegate. I could do this by making the function literal include the null-checking code, but is there maybe a better solution to this problem? The delegate is supposed to change a variable within the D class. Hope you understand it :) A delegate is a struct with a data pointer and a function pointer. You can access the individual parts via .ptr and .func (I believe). You can even change them via those properties. does that help? -Steve I did read that part. The problem lies more in that I'd like to point to something which is not there yet. In the code 'c.method()' is not there yet, as c is null. Maybe I should create a dummy object for c to point to in stead of null ? That way I point the delegate to the dummy method and ignore it as long as it is pointing to the dummy method :) The only drawback to this is that all objects I want to point the delegate to, need to somehow be convertable to the dummy type (interface/abstract class), meaning it will be less flexible.
Re: delegate !is null
On Tue, 08 Sep 2009 09:22:30 -0400, Saaa em...@needmail.com wrote: Steven Schveighoffer schvei...@yahoo.com wrote in message news:op.uzxs4wyreav...@localhost.localdomain... On Sun, 06 Sep 2009 18:54:47 -0400, Saaa em...@needmail.com wrote: I'd like to set D's delegate to a method which is not yet available (like c.method). I solved this by encapsulating the method within a function literal, but I also need to know whether the method is available or not when calling the delegate. I could do this by making the function literal include the null-checking code, but is there maybe a better solution to this problem? The delegate is supposed to change a variable within the D class. Hope you understand it :) A delegate is a struct with a data pointer and a function pointer. You can access the individual parts via .ptr and .func (I believe). You can even change them via those properties. does that help? -Steve I did read that part. The problem lies more in that I'd like to point to something which is not there yet. In the code 'c.method()' is not there yet, as c is null. Maybe I should create a dummy object for c to point to in stead of null ? That way I point the delegate to the dummy method and ignore it as long as it is pointing to the dummy method :) The only drawback to this is that all objects I want to point the delegate to, need to somehow be convertable to the dummy type (interface/abstract class), meaning it will be less flexible. Hm... I'm still confused. Why not just set the delegate to null? Why do you need to have the delegate set to something? There are ways to do it, without having a class instance, but it is messy. -Steve
Re: delegate !is null
The problem lies more in that I'd like to point to something which is not there yet. In the code 'c.method()' is not there yet, as c is null. Maybe I should create a dummy object for c to point to in stead of null ? That way I point the delegate to the dummy method and ignore it as long as it is pointing to the dummy method :) The only drawback to this is that all objects I want to point the delegate to, need to somehow be convertable to the dummy type (interface/abstract class), meaning it will be less flexible. Hm... I'm still confused. Why not just set the delegate to null? Why do you need to have the delegate set to something? It is for the gui. I give it a list of things to display. And some of these things don't yet exist or can be deleted at any time. I'd like it to display the last valid value. There are ways to do it, without having a class instance, but it is messy. how messy? :D Kind of related: If you delete an object and later create a new object, what are the chances they are located on the same place (deleted.ptr is new.ptr) ? Does the garbage collector try to reuse locations or is it the opposite (or random) ?
Re: delegate !is null
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Saaa wrote: The problem lies more in that I'd like to point to something which is not there yet. In the code 'c.method()' is not there yet, as c is null. Maybe I should create a dummy object for c to point to in stead of null ? That way I point the delegate to the dummy method and ignore it as long as it is pointing to the dummy method :) The only drawback to this is that all objects I want to point the delegate to, need to somehow be convertable to the dummy type (interface/abstract class), meaning it will be less flexible. Hm... I'm still confused. Why not just set the delegate to null? Why do you need to have the delegate set to something? It is for the gui. I give it a list of things to display. And some of these things don't yet exist or can be deleted at any time. I'd like it to display the last valid value. There are ways to do it, without having a class instance, but it is messy. how messy? :D The only way I've found so far to do static binding like you are talking about is using string mixins. My port of Atl's window classes uses a MFC like message map: mixin messageMap!( msgRangeHdlr!(WM_MOUSEFIRST, WM_MOUSELAST, wmMouseEvents), msgHdlr!(WM_PAINT, wmPaint), msgHdlr!(WM_SIZE, wmSize), msgHdlr!(WM_KEYUP, wmKeyUp), msgHdlr!(WM_CHAR, wmChar), msgHdlr!(WM_SHOWWINDOW, wmShow), msgHdlr!(WM_CLOSE, wmClose), msgHdlr!(WM_CREATE, wmCreate) ); Having to put the classes method in a string is a bit ugly, but without c++ style pointer to members I don't see any other way of doing it. If you want to have a look in more detail: http://www.sstk.co.uk/atlWinD.php Kind of related: If you delete an object and later create a new object, what are the chances they are located on the same place (deleted.ptr is new.ptr) ? Does the garbage collector try to reuse locations or is it the opposite (or random) ? Dunno, but the full source code is in dmd zip @ src\druntime\src\gc\basic\gcx.d if you are really that interested. - -- My enormous talent is exceeded only by my outrageous laziness. http://www.ssTk.co.uk -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.7 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iD8DBQFKppg7T9LetA9XoXwRApS4AJ0f+SI6MhonTiwLqC6LPD1lq4GzUACfU/oC TY+3D6isjNKUt9zVxgoSDJ4= =foxA -END PGP SIGNATURE-
Re: delegate !is null
On Tue, 08 Sep 2009 12:40:13 -0400, Saaa em...@needmail.com wrote:
Hm... I'm still confused. Why not just set the delegate to null? Why
do
you need to have the delegate set to something?
It is for the gui. I give it a list of things to display.
And some of these things don't yet exist or can be deleted at any time.
I'd like it to display the last valid value.
That still doesn't explain why you need to have delegates set to something
valid, yet have a null pointer value. Either a) you are trying to subvert
the type system, or b) you can simply set the whole delegate (function and
pointer) once you get the class instance.
It's hard for me to say what is the best way to do it, but generally,
things like this are difficult, and rightfully so. Having a delegate
without a valid pointer makes little sense.
There are ways to do it, without having a class instance, but it is
messy.
how messy? :D
class C
{
int val = 0;
int method() {return val;}
}
int delegate() dg;
dg.func = C.method; // note the upper-case C
// dg is now a instanceless delegate to C.method.
dg.ptr = new C;
Now you can call dg() and it will call the C.method function on the newly
created C object.
Note that this method of manipulating methods does NOT obey inheritance.
For example:
class B : C
{
int method() {return 555;}
}
dg.ptr = new B;
dg(); // will return 0, since it calls C's version of method.
I also don't know how well it will work on interfaces.
Kind of related:
If you delete an object and later create a new object, what are the
chances
they are located on the
same place (deleted.ptr is new.ptr) ?
Does the garbage collector try to reuse locations or is it the opposite
(or
random) ?
The chances are non-zero :) I wouldn't depend on this behavior either way
if I were you.
-Steve
Re: delegate !is null
On Tue, 08 Sep 2009 16:15:49 -0400, Saaa em...@needmail.com wrote: // dg is now a instanceless delegate to C.method. dg.ptr = new C; So, nothing special under the hood, this would also work? C c= new C; dg.ptr = c; Yes, same thing. I also don't know how well it will work on interfaces. Very nice :) Might be useful, thanks. Just be cautious. You can get into undefined territory real easily, because dg.ptr is a void * (i.e. goodbye type system, I'm on my own!) Kind of related: If you delete an object and later create a new object, what are the chances they are located on the same place (deleted.ptr is new.ptr) ? Does the garbage collector try to reuse locations or is it the opposite (or random) ? The chances are non-zero :) Are you quite sure there? very quite. I'm only asking a single 'new'. I mean, there could be some heuristic which would prevent the a new object to take the place of the latest deleted one. There isn't. Memory freed by the GC is able to be used in another allocation. If this didn't happen, then it wouldn't take long to use up all the memory in the system. I'm sure if you threw random shit at the GC long enough, it would do this :) -Steve
Re: delegate !is null
Hm... I'm still confused. Why not just set the delegate to null? Why
do
you need to have the delegate set to something?
It is for the gui. I give it a list of things to display.
And some of these things don't yet exist or can be deleted at any time.
I'd like it to display the last valid value.
That still doesn't explain why you need to have delegates set to something
valid, yet have a null pointer value.
Either a) you are trying to subvert the type system, or b) you can simply
set the whole delegate (function and pointer) once you get the class
instance.
It's hard for me to say what is the best way to do it, but generally,
things like this are difficult, and rightfully so. Having a delegate
without a valid pointer makes little sense.
There are ways to do it, without having a class instance, but it is
messy.
how messy? :D
class C
{
int val = 0;
int method() {return val;}
}
int delegate() dg;
dg.func = C.method; // note the upper-case C
That's actually quite nice, I didn't know it worked like that :)
// dg is now a instanceless delegate to C.method.
dg.ptr = new C;
So, nothing special under the hood, this would also work?
C c= new C;
dg.ptr = c;
Now you can call dg() and it will call the C.method function on the newly
created C object.
Note that this method of manipulating methods does NOT obey inheritance.
For example:
class B : C
{
int method() {return 555;}
}
dg.ptr = new B;
dg(); // will return 0, since it calls C's version of method.
I also don't know how well it will work on interfaces.
Very nice :)
Might be useful, thanks.
Kind of related:
If you delete an object and later create a new object, what are the
chances
they are located on the
same place (deleted.ptr is new.ptr) ?
Does the garbage collector try to reuse locations or is it the opposite
(or
random) ?
The chances are non-zero :)
Are you quite sure there?
I'm only asking a single 'new'.
I mean, there could be some heuristic which would prevent the a new object
to take the place of the latest deleted one.
I wouldn't depend on this behavior either way if I were you.
Yeah you're right, as long as something like this isn't part of the spec it
wouldn't be safe.
Plus it shouldn't be part of the spec as it would be too stringent on the gc
implementation in my opinion.
Just curious :)
Re: delegate !is null
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Saaa wrote: The only way I've found so far to do static binding like you are talking about is using string mixins. I need to rethink stuff a bit, but mixins might be the solution. My port of Atl's window classes uses a MFC like message map: mixin messageMap!( msgRangeHdlr!(WM_MOUSEFIRST, WM_MOUSELAST, wmMouseEvents), msgHdlr!(WM_PAINT, wmPaint), msgHdlr!(WM_SIZE, wmSize), msgHdlr!(WM_KEYUP, wmKeyUp), msgHdlr!(WM_CHAR, wmChar), msgHdlr!(WM_SHOWWINDOW, wmShow), msgHdlr!(WM_CLOSE, wmClose), msgHdlr!(WM_CREATE, wmCreate) ); Having to put the classes method in a string is a bit ugly, but without c++ style pointer to members I don't see any other way of doing it. If you want to have a look in more detail: http://www.sstk.co.uk/atlWinD.php The zip 404ed Typeof. doh. fixed. - -- My enormous talent is exceeded only by my outrageous laziness. http://www.ssTk.co.uk -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.7 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iD8DBQFKpuNnT9LetA9XoXwRAuutAKC0q9CzjrH37nOXhg5eJNaWMw1X8wCdFa0P QNhCcfUJamdDdU2/n6LAg/U= =B9aH -END PGP SIGNATURE-
Re: delegate !is null
Steven Schveighoffer schvei...@yahoo.com wrote in message
news:op.uzqxxo1neav...@localhost.localdomain...
On Fri, 04 Sep 2009 14:33:12 -0400, Saaa em...@needmail.com wrote:
class C
{
private int i;
int method()
{
return i;
}
}
class D
{
private int delegate(void) _deleg;
this(int delegate(void) d)
{
_deleg = d;
}
void write()
{
if(_deleg !is null)
}
writef(_deleg());
}
}
}
C c = null;
D d = new d;
d.function(c.method());
//This fails, as method is not availible for null.
d.function({return c.method();});
//This works but now I can't check whether c is null or not.
d.write(); //will fail.
Any suggestions?
Maybe you could rephrase your question in english. I can't really
understand what you are trying to do with this code.
i.e. I want to be able to tell whether a delegate is null or not, how do
I do that. But you do that just like you said -- dg !is null.
-Steve
(unexpected visit this weekend)
Erm, like this.. ?
I'd like to set D's delegate to a method which is not yet available (like
c.method).
I solved this by encapsulating the method within a function literal, but I
also need to know whether
the method is available or not when calling the delegate.
I could do this by making the function literal include the null-checking
code, but is there maybe a better solution to this problem?
The delegate is supposed to change a variable within the D class.
Hope you understand it :)
