• Enjoys Math (27/27) Sep 04 2022 I have the following MWE:
• Enjoys Math (4/31) Sep 04 2022 Okay... now the MWE works as I expected polymorphism to work, but
• Enjoys Math (4/42) Sep 04 2022 Here is a link to the library on github. Please help me solve
• Enjoys Math (6/50) Sep 04 2022 Simply git clone it and run from main.d or hit debug in VisualD
• Enjoys Math (2/22) Sep 04 2022 Fixed. I was simply not implementing anything in the subclass.
• rikki cattermole (27/27) Sep 04 2022 This appears to be working correctly.

Enjoys Math <enjoysmath gmail.com> writes:

I have the following MWE:

```
import std.exception;
import std.stdio;

abstract class B
{
    B opCall() {
       throw new Exception("NotImplemented");
    }
}

class A : B
{
    override B opCall() {
       return new A();
    }
}

int main() {
    B a = new A();
    a();
    readln();
    return 0;
}

```

But B.opCall() gets called!   I thought polymorphism was cool 
until now....

How can I get this to work the way I expected it to?  Would an 
abstract method in base do it?

Enjoys Math <enjoysmath gmail.com> writes:

On Sunday, 4 September 2022 at 17:36:24 UTC, Enjoys Math wrote:
 I have the following MWE:

 ```
 import std.exception;
 import std.stdio;

 abstract class B
 {
    B opCall() {
       throw new Exception("NotImplemented");
    }
 }

 class A : B
 {
    override B opCall() {
       return new A();
    }
 }

 int main() {
    B a = new A();
    a();
    readln();
    return 0;
 }

 ```

 But B.opCall() gets called!   I thought polymorphism was cool 
 until now....

 How can I get this to work the way I expected it to?  Would an 
 abstract method in base do it?

Okay... now the MWE works as I expected polymorphism to work, but 
my complicated library is not doing it right...

:\

Enjoys Math <enjoysmath gmail.com> writes:

On Sunday, 4 September 2022 at 17:38:54 UTC, Enjoys Math wrote:
 On Sunday, 4 September 2022 at 17:36:24 UTC, Enjoys Math wrote:
 I have the following MWE:

 ```
 import std.exception;
 import std.stdio;

 abstract class B
 {
    B opCall() {
       throw new Exception("NotImplemented");
    }
 }

 class A : B
 {
    override B opCall() {
       return new A();
    }
 }

 int main() {
    B a = new A();
    a();
    readln();
    return 0;
 }

 ```

 But B.opCall() gets called!   I thought polymorphism was cool 
 until now....

 How can I get this to work the way I expected it to?  Would an 
 abstract method in base do it?

 Okay... now the MWE works as I expected polymorphism to work, 
 but my complicated library is not doing it right...

 :\

Here is a link to the library on github.  Please help me solve 
this!! :D

https://github.com/enjoysmath/diagram-chaser

Enjoys Math <enjoysmath gmail.com> writes:

On Sunday, 4 September 2022 at 17:43:33 UTC, Enjoys Math wrote:
 On Sunday, 4 September 2022 at 17:38:54 UTC, Enjoys Math wrote:
 On Sunday, 4 September 2022 at 17:36:24 UTC, Enjoys Math wrote:
 I have the following MWE:

 ```
 import std.exception;
 import std.stdio;

 abstract class B
 {
    B opCall() {
       throw new Exception("NotImplemented");
    }
 }

 class A : B
 {
    override B opCall() {
       return new A();
    }
 }

 int main() {
    B a = new A();
    a();
    readln();
    return 0;
 }

 ```

 But B.opCall() gets called!   I thought polymorphism was cool 
 until now....

 How can I get this to work the way I expected it to?  Would 
 an abstract method in base do it?

 Okay... now the MWE works as I expected polymorphism to work, 
 but my complicated library is not doing it right...

 :\

 Here is a link to the library on github.  Please help me solve 
 this!! :D

 https://github.com/enjoysmath/diagram-chaser

Simply git clone it and run from main.d or hit debug in VisualD 
to see my problem.  It's calling the base class method which 
throws a NotImplemented exception, but it should be calling one 
of the derived subclasses.  I will keep coding on it and update 
the code, but if I get it fixed, I'll post an update here.

Enjoys Math <enjoysmath gmail.com> writes:

On Sunday, 4 September 2022 at 17:50:10 UTC, Enjoys Math wrote:
 On Sunday, 4 September 2022 at 17:43:33 UTC, Enjoys Math wrote:
 On Sunday, 4 September 2022 at 17:38:54 UTC, Enjoys Math wrote:
 On Sunday, 4 September 2022 at 17:36:24 UTC, Enjoys Math 
 wrote:
 [...]

 Okay... now the MWE works as I expected polymorphism to work, 
 but my complicated library is not doing it right...

 :\

 Here is a link to the library on github.  Please help me solve 
 this!! :D

 https://github.com/enjoysmath/diagram-chaser

 Simply git clone it and run from main.d or hit debug in VisualD 
 to see my problem.  It's calling the base class method which 
 throws a NotImplemented exception, but it should be calling one 
 of the derived subclasses.  I will keep coding on it and update 
 the code, but if I get it fixed, I'll post an update here.

Fixed.  I was simply not implementing anything in the subclass.

rikki cattermole <rikki cattermole.co.nz> writes:

This appears to be working correctly.

You override the implementation of opCall in A, so when you called 
opCall, it called the implementation of it in A. B's opCall never landed 
in the vtable.

It does in fact return an A object.

```d
import std.stdio;

abstract class B
{
    B opCall() {
       throw new Exception("NotImplemented");
    }
}

class A : B
{
    override B opCall() {
       return new A();
    }
}

int main() {
    B a = new A();

    auto got = a();
    assert(got !is null);
    writeln(got);

    return 0;
}
```