Hey,

I recently read an interesting blog Why should I have written ZeroMQ in C, not C++ (part II) by Martin Sústrik. The title is misleading; to me its main observation is that object oriented program may not lead to the most performant implementation. After reading the blog I asked myself I would I implement this in D? I thought we could use mixin and template mixin to implement this in a more manageable/scalable way. The complete source code is at Embedded Container.

To make a type "double linkable" the developer needs to mixin the following mixin template:

mixin template DoubleLinkable()
{
  typeof(this) next;
  typeof(this) prev;
}

The next and prev pointer can be access with the help of mixin by using the following templates:

T* next(T, string name)(T node) pure nothrow const 
{ 
  mixin("return &(node." ~ name ~ ".next);"); 
} 
  
T* prev(T, string name)(T node) pure nothrow const 
{ 
  mixin("return &(node." ~ name ~ ".prev);"); 
}

To use the above abstraction the developer just needs to do the following:

class Person
{
  int age;
  int weight;
  mixin DoubleLinkable people;
} 
 
void main()
{
  auto list = new DoubleLinkedList!(Person, "people")();

  auto person1 = new Person(6, 60);
  list.pushFront(person1);

  auto person2 = new Person(25, 160);
  list.pushFront(person2);

  auto person3 = new Person(11, 100);
  list.pushFront(person3);

  list.erase(person2);
  list.erase(person3);
  list.erase(person1);
}


I am not a big fan of the template signature 'class DoubleLinkedList(T, string name)' but I couldn't figure out a better way of allowing one object to be embedded in multiple containers. Thoughts? Any idea how this can be improved so that it is easier to use and read?

Thanks,
-Jose