www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - Using DLLs to extend an existing class

reply Sebastian Trent <null null.com> writes:
I'm developing a plugin system for a D program.

I have a complex class hierarchy which will be complied into our 
executable, and I want
third parties to be able to further extend it with their own DLLs 
- subject to implementing an API present in the most derived 
class - which will be provided to the user as a auto generated 
header (.di) file using "dmd -H [modules]"

For example, in our program:

class A
     //Protected and public methods

class B : A
     //Protected and public methods.

     public string apiMethod()
         return "Class B";


And in a typical "Dll to be' plugin:


import B; //Currently using a 'header' file generated with dmd -H 

mixin dllBoilerplate;

export class C : B
    //Public (export?) API implimentation
     override public string apiMethod()
         return "Class C";

    //Private methods

Currently, when I try to compile the plugin DLL, I get linker 
errors that mangled symbol for apiMethod is not defined - These 
are the symbols defined in the header (b.di) file, but are not 
implemented: by definition intended to be part of the main 
program, instead.

Can anyone explain how I should go about building the plugin - I 
suspect it involved what I am and am not declaring 'export', but 
I'm unable to find any material that puts light on my situation.


Dec 19 2017
parent rikki cattermole <rikki cattermole.co.nz> writes:
I am afraid to say this has quite a simple answer.

TypeInfo (and with that vtables used as part of classes), do not cross 
the dll boundary (other platforms things mostly work).

Which means, can't do what you are wanting I'm afraid.

It is an implementation issue that we REALLY REALLY REALLY need to fix.
Dec 19 2017