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D - Overloading "delete"

reply Sam McCall <tunah.d tunah.net> writes:
The "delete" operator is used to delete key/value pairs from associative 
arrays. Could it be made possible to overload this, so I can have
delete myList[i];
in a custom list class? (maybe this should be possible for arrays too, 
inefficient though).
It seems like a special case keyword that could better be used more 
generally.
Sam
Feb 09 2004
parent reply J Anderson <REMOVEanderson badmama.com.au> writes:
Sam McCall wrote:


 The "delete" operator is used to delete key/value pairs from 
 associative arrays. Could it be made possible to overload this, so I 
 can have
 delete myList[i];
 in a custom list class? (maybe this should be possible for arrays too, 
 inefficient though).
 It seems like a special case keyword that could better be used more 
 generally.
 Sam


You could always use a proxy object.

-- 
-Anderson: http://badmama.com.au/~anderson/
Feb 09 2004
parent reply Sam McCall <tunah.d tunah.net> writes:
J Anderson wrote:


 Sam McCall wrote:
 

 The "delete" operator is used to delete key/value pairs from 
 associative arrays. Could it be made possible to overload this, so I 
 can have
 delete myList[i];
 in a custom list class? (maybe this should be possible for arrays too, 
 inefficient though).
 It seems like a special case keyword that could better be used more 
 generally.
 Sam


 
 
 You could always use a proxy object.
 


Or just use myList.delete(i). I was just thinking it might be nice for 
consistency.

Or maybe not, dmd doesn't think much of my coding. I was quite taken 
aback when this code:
Iterator!(T) it=iterator();
...
if(it is ListIterator!(T))

elicited this error message:
collections.d(129): interface ListIterator has no value

Still puzzling over that one :)
Sam
Feb 10 2004
next sibling parent reply Carlos Santander B. <Carlos_member pathlink.com> writes:
In article <c0aac3$esq$1 digitaldaemon.com>, Sam McCall says...

Or just use myList.delete(i). I was just thinking it might be nice for 
consistency.

Or maybe not, dmd doesn't think much of my coding. I was quite taken 
aback when this code:
Iterator!(T) it=iterator();
...
if(it is ListIterator!(T))

elicited this error message:
collections.d(129): interface ListIterator has no value

Still puzzling over that one :)
Sam


I don't remember who told you that, but the 'is' operator is the same as the
'==='. If you want to check if 'it' is a ListIterator, do a cast.

-----------------------
Carlos Santander Bernal
Feb 10 2004
parent Sam McCall <tunah.d tunah.net> writes:
Carlos Santander B. wrote:


 I don't remember who told you that, but the 'is' operator is the same as the
 '==='. If you want to check if 'it' is a ListIterator, do a cast.


Oops... I saw someone discussing an is or isa operator (like 
instanceof), and then i saw "is" in the spec and jumped to conclusions :(
Sam
Feb 10 2004
prev sibling parent reply J Anderson <REMOVEanderson badmama.com.au> writes:
Sam McCall wrote:


 J Anderson wrote:


 Sam McCall wrote:


 The "delete" operator is used to delete key/value pairs from 
 associative arrays. Could it be made possible to overload this, so I 
 can have
 delete myList[i];
 in a custom list class? (maybe this should be possible for arrays 
 too, inefficient though).
 It seems like a special case keyword that could better be used more 
 generally.
 Sam




 You could always use a proxy object.


 Or just use myList.delete(i). I was just thinking it might be nice for 
 consistency.

 Or maybe not, dmd doesn't think much of my coding. I was quite taken 
 aback when this code:
 Iterator!(T) it=iterator();
 ....
 if(it is ListIterator!(T))

 elicited this error message:
 collections.d(129): interface ListIterator has no value

 Still puzzling over that one :)
 Sam



I think it would be a good idea to be able to be able to handle deletes 
of blocks of objects.  Also, proxy objects are often more work then it's 
worth.

-- 
-Anderson: http://badmama.com.au/~anderson/
Feb 10 2004
parent reply "C" <dont respond.com> writes:
What is a proxy object ?

C
"J Anderson" <REMOVEanderson badmama.com.au> wrote in message
news:c0c3f0$9vn$1 digitaldaemon.com...

 Sam McCall wrote:


 J Anderson wrote:


 Sam McCall wrote:


 The "delete" operator is used to delete key/value pairs from
 associative arrays. Could it be made possible to overload this, so I
 can have
 delete myList[i];
 in a custom list class? (maybe this should be possible for arrays
 too, inefficient though).
 It seems like a special case keyword that could better be used more
 generally.
 Sam




 You could always use a proxy object.


 Or just use myList.delete(i). I was just thinking it might be nice for
 consistency.

 Or maybe not, dmd doesn't think much of my coding. I was quite taken
 aback when this code:
 Iterator!(T) it=iterator();
 ....
 if(it is ListIterator!(T))

 elicited this error message:
 collections.d(129): interface ListIterator has no value

 Still puzzling over that one :)
 Sam



 I think it would be a good idea to be able to be able to handle deletes
 of blocks of objects.  Also, proxy objects are often more work then it's
 worth.

 -- 
 -Anderson: http://badmama.com.au/~anderson/
Feb 12 2004
parent J Anderson <REMOVEanderson badmama.com.au> writes:
C wrote:


What is a proxy object ?

C
  


It's an object that is used in the place of another object (kinda like 
boxing). It's kinda like a object that sits in between operations. 
However, I assumpted because it works in C++ it would work in D. However 
as the below example shows it doesn't work.  I don't know if this is a 
bug or by-design. I'm going to summit it as a bug anyways.

Well in the current example (note code below doesn't work):

import std.c.stdio;

template ListT(T)
{
    class Proxy
    {
        this(List thelist, int i) { list = thelist; index = i;}
        ~this() { list.remove(index); }
       
        //T get() { return T; }
       
    private:
        List list;
        int index;
    }
   
    class List
    {
        T [] List;
       
        void add(T t) { List ~= t;    }
       
        void remove(int i)
        { 
            printf("remove %d\n", i);
            //...
        }
       
        Proxy opIndex(int i)
        {
            Proxy proxy = new Proxy(this, i);
            return proxy;
        }
    }
}


int main ( char [] [] args )
{
    ListT!(int).List test = new ListT!(int).List();
    test.add(10);
    test.add(20);
    test.add(30);
    delete test[1]; //Doesn't work (C:\Program 
Files\DIDE\Projects\test66\test66.d(52): 'test.opIndex(1)' is not an lvalue)

    return 1;
}


-- 
-Anderson: http://badmama.com.au/~anderson/
Feb 12 2004