How to use interface template? How to model interface template properly in D.

[Matthew Ong]

Hi All,

The main aim here is to find out how to model similar syntax within D.

Due to the nature of the architecture of the library that I have 
designed in Java and heavily leans towards interface generics.
It works well with java.

Yes. I am aware about Tuple to allow me to do multiple value return.
The point is Not about returning multiple, but how to moduel

public interface DefType1<T1> { // Please note this is like interface 
template
     public Throwable getError();
     public T1 getValue();
     public String getDesc();
}
// Elsewhere.

public class RetVal1<T1> implements DefType1<T1> {

     private RetVal1() {
     }

     public static <T1> RetVal1<T1> make(T1 value) {
         RetVal1<T1> obj = new RetVal1<T1>();
         obj.mValue = value;
         return obj;
     }

     private Throwable mError;

     public void setError(Throwable error) {
         mError = error;
     }

     public Throwable getError() {
         return mError;
     }
     private T1 mValue;

     public T1 getValue() {
         return mValue;
     }
     private String mDesc;

     public String getDesc() {
         return mDesc;
     }
}

// Yet, else where
class Account{...}

  public static RetVal1<Account> methodA(int num, String str) { // 
similar to Instantiation template
          ... // do something.
         return RetVal2.<Account>make(num, str);
     }

void main(string[] args){
   RetVal1<Account> ret = methodA(1, "abc"); // some method call that return
   if(ret.getError()==null){
      Account acc=ret.getValue1();
      prnln("amount=" + acc.getAmount());
   }
}
http://www.digitalmars.com/d/2.0/template.html#Constraint
Struct, Union, and Interface Templates
...
Analogously to class templates, struct, union and interfaces can be 
transformed into templates by supplying a template parameter list.
However there is no example shown.
In D the syntax should more or less look similar:

interface DefType1(T1) { // No issue here
  	public:
     Throwable getError();
     T1 getValue();
     String getDesc();
}

public class RetVal1(T1) : DefType1(T1) { // ### or IS IT: DefType1!(T1) ??
...
    public static RetVal1(T1) make(T1)(T1 value) { // static method template
         RetVal1(T1) obj = new RetVal1(T1)(); // ### or IS IT: new 
RetVal1!(T1)();
         obj.mValue = value;
         return obj;
    }
...
}


public static RetVal1(Account) methodA(int num, String str) { //### How 
to do that?? Compilation error.
    Account acc=new Account();
    ... // do something.
    return RetVal2.(Account)make(ac); //### How to do that?? compilation 
error also
}

  RetVal1(Account) ret = methodA(1, "abc"); // Compilation error also.
   if(ret.getError()==null){
      Account acc=ret.getValue1();
      prnln("amount=" + acc.getAmount());
   }
------------------------------------------------------------------------
Kindly show some compilable and working code sample.

Thanks very much.

-- 
Matthew Ong
email: ongbp at yahoo.com