Alternatives to OOP in D

[Brother Bill]

I have heard that there are better or at least alternative ways 
to have encapsulation, polymorphism and inheritance outside of 
OOP.

With OOP in D, we have full support for Single Inheritance, 
including for Design by Contract (excluding 'old').  D also 
supports multiple Interfaces.

What would be the alternatives and why would they be better?
I assume the alternatives would have
1. Better performance
2. Simpler syntax
3. Easier to read, write and maintain

If possible, please provide links to documentation or examples.