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digitalmars.D.learn - "extending" existed class

reply novice2 <sorry noem.ail> writes:
Hello.
I have existed class (for example Stream in phobos), and i need add
new method to it. In the past (if i correctly remember), i was able
to do it by defining function, that accept instance of class as
first argument, and then use it function like instance.function()

Now (DMD 1.70) i can't compile this code:

//////////////////////////////
class A
{
  int method1() { return 1; }
}

int method2(A a)
{
  return 2;
}

void main()
{
   A a = new A;
   int i = a.method1();
   int k = a.method2();
}
//////////////////////////////

Compiler say
1.d(20): no property 'method2' for type '1.A'

Can anyone say, what i missed, or the better way to "extend"
existed class without declare new class based on existed?
Thanks.
Oct 18 2006
next sibling parent reply "Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:
"novice2" <sorry noem.ail> wrote in message 
news:eh4u36$2bsc$1 digitaldaemon.com...

 Hello.
 I have existed class (for example Stream in phobos), and i need add
 new method to it. In the past (if i correctly remember), i was able
 to do it by defining function, that accept instance of class as
 first argument, and then use it function like instance.function()
...
 Can anyone say, what i missed, or the better way to "extend"
 existed class without declare new class based on existed?
 Thanks.



I don't think that ability has ever existed.  Maybe you're confusing it with 
the ability to do so with arrays?

int method(int[] x)
{
 return x.length;
}

void main()
{
 int[] arr = new int[10];
 int i = method(arr);
 int k = arr.method(); // equivalent to above
}
Oct 18 2006
parent reply novice2 <sorry noem.ail> writes:
Jarrett Billingsley (kb3ctd2 yahoo.com) 2006/10/18 08:49
I don't think that ability has ever existed.  Maybe you're confusing it with
the ability to do so with arrays?



Ah.. Only for arrays :(
Thank you for information.

Sorry for dumb question, but are there any
other ways to "extend" existed classes?
Inheritance only?
Oct 18 2006
parent "Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:
"novice2" <sorry noem.ail> wrote in message 
news:eh5hi3$2v32$1 digitaldaemon.com...

 Ah.. Only for arrays :(
 Thank you for information.

 Sorry for dumb question, but are there any
 other ways to "extend" existed classes?
 Inheritance only?



Yep.  Some people have proposed something found in C#, where you can add 
methods to classes from outside the class, like:

class C
{
    int method()
    {
        return 10;
    }
}

int C.method2()
{
    return 20;
}

C c = new C();
c.method();
c.method2();

But this is not possible in D.
Oct 18 2006
prev sibling parent reply Lionello Lunesu <lio lunesu.remove.com> writes:
novice2 wrote:

 Hello.
 I have existed class (for example Stream in phobos), and i need add
 new method to it. In the past (if i correctly remember), i was able
 to do it by defining function, that accept instance of class as
 first argument, and then use it function like instance.function()
 
 Now (DMD 1.70) i can't compile this code:
 
 //////////////////////////////
 class A
 {
   int method1() { return 1; }
 }
 
 int method2(A a)
 {
   return 2;
 }
 
 void main()
 {
    A a = new A;
    int i = a.method1();
    int k = a.method2();
 }
 //////////////////////////////
 
 Compiler say
 1.d(20): no property 'method2' for type '1.A'
 
 Can anyone say, what i missed, or the better way to "extend"
 existed class without declare new class based on existed?
 Thanks.



It is, and was, only possible for arrays. But I sure wish it was 
possible for all types (classes, but int/float/etc too!)

L.
Oct 18 2006
next sibling parent Bill Baxter <wbaxter gmail.com> writes:
Lionello Lunesu wrote:

 novice2 wrote:
 

 Hello.
 I have existed class (for example Stream in phobos), and i need add
 new method to it. In the past (if i correctly remember), i was able
 to do it by defining function, that accept instance of class as
 first argument, and then use it function like instance.function()

 Now (DMD 1.70) i can't compile this code:

 //////////////////////////////
 class A
 {
   int method1() { return 1; }
 }

 int method2(A a)
 {
   return 2;
 }

 void main()
 {
    A a = new A;
    int i = a.method1();
    int k = a.method2();
 }
 //////////////////////////////

 Compiler say
 1.d(20): no property 'method2' for type '1.A'

 Can anyone say, what i missed, or the better way to "extend"
 existed class without declare new class based on existed?
 Thanks.



 
 It is, and was, only possible for arrays. But I sure wish it was 
 possible for all types (classes, but int/float/etc too!)
 
 L.



Argh!  Why so many special case rules for arrays?!

--bb
Oct 18 2006
prev sibling parent reply Bill Baxter <wbaxter gmail.com> writes:
Lionello Lunesu wrote:

 novice2 wrote:

 Compiler say
 1.d(20): no property 'method2' for type '1.A'

 Can anyone say, what i missed, or the better way to "extend"
 existed class without declare new class based on existed?
 Thanks.



 
 It is, and was, only possible for arrays. But I sure wish it was 
 possible for all types (classes, but int/float/etc too!)



By the way, where is that fun feature for arrays documented?  I can't 
seem to find it anywhere in the D spec at http://www.digitalmars.com/d/.

--bb
Oct 18 2006
parent reply Hasan Aljudy <hasan.aljudy gmail.com> writes:
Bill Baxter wrote:

 By the way, where is that fun feature for arrays documented?  



It's not! (that's the most fun part!)
Oct 18 2006
parent Bill Baxter <dnewsgroup billbaxter.com> writes:
Hasan Aljudy wrote:

 Bill Baxter wrote:

 By the way, where is that fun feature for arrays documented?  



 It's not! (that's the most fun part!)



Must be to encourage everyone to read and participate in the news 
groups.  :-)
Oct 18 2006