Hi, below is an example of DI-dependency injection with 3 versions nested in the code. If you remove the leading // characters, you will not get the "no property deliver for service of type object.Object" error. Because version-2I with interface wants its methods to depend on Object..

//abstract class /* toggle-code
interface //* ^---version 2A */
ITransport
{
  string deliver();
}

class Ship : ITransport
{
  override string deliver()
  {
    return "Ship Deliver";
  }
}

class Truck : ITransport
{
  override string deliver()
  {
    return "Truck Deliver";
  }
}

abstract class Logistics
{
  ITransport createTransport();

  auto operations()
  {
    return createTransport.deliver();
  }
}

class RoadLogistics : Logistics
{
  override ITransport createTransport()
  {
    return new Truck();
  }
}

class SeaLogistics : Logistics
{
  override ITransport createTransport()
  {
    return new Ship();
  }
}

import std.stdio;
void main()
{
  // DI version 1:
  auto sl = new SeaLogistics;
  auto rl = new RoadLogistics;

  auto logistics = [ sl, rl ];
  foreach(deliver; logistics)
  {
    auto str = deliver.operations();
    str.length.writeln(": ", str);
  }

  import std.range : repeat;
  "÷ ".repeat(9).writefln!"%-(%s%)";

  // A->I version 2:
  auto truck = new Truck;
  auto ship = new Ship;

  auto services = [ truck, ship ];
  foreach(service; services)
  {
    auto str = service.deliver();
    str.length.writeln(": ", str);
  }
}

Maybe using an abstract class instead of interface or not using auto will solve the problem, but I can't accept the situation! I wonder what makes the interface special?

SDB@79

On Sunday, 18 June 2023 at 16:58:15 UTC, Ali Çehreli wrote:

This is very interesting because it looks like a bug. Why is there no problem in an abstracted object, but things get confused in the interface (ITransport)?

On Sunday, 18 June 2023 at 16:58:15 UTC, Ali Çehreli wrote:

In fact, there is no need to cast:

interface ITransport
{
  string deliver();
}

//...

void main()
{
  auto truck = new Truck;
  ITransport ship = new Ship;

/* or
  ITransport truck = new Truck;
  auto ship = new Ship;

// or

  ITransport truck = new Truck;
  ITransport ship = new Ship;//*/
}

SDB@78