Structure's inheritance

[Dicebot]

I believe template mixin are the way to go for structs. Small 
annotated example:

// http://dpaste.1azy.net/56dd2513

mixin template Operators()
{
	// Verify "a" field exists for better compile-time error. 
Hard-coded here.
	// As an alternative, name of field to use can be provided as a 
template argument.
	static assert(is(typeof(typeof(this).init.a)),
		"class/struct that used this template mixin must have 'a' 
member declared");
	
	// Simple implementation for opBinary. As template mixins use 
scope of instatiator,
	// "this" will have target class/struct	type. Basically, you can 
write here any
	// implementation you would normally do in a base class.
	typeof(this) opBinary(string op)(typeof(this) rhs)
		if (op == "+")
	{
		return Test(this.a + rhs.a);
	}
}

struct Test
{
	int a;
	
	// that simple, almost same code amount as with "Test : TestBase"
	mixin Operators;
}

void main()
{
	Test x1 = { 2 };
	Test x2 = { 3 };
	import std.stdio;
	// prints "Test(5)"
	writeln(x1 + x2);
}