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digitalmars.D.learn - Virtual nested classes and "this"


I have been poking around with overriding internal classes, and 
after reading [1] it was actually not clear to me whether it 
could be done or not, so I started trying.

The good news (for me, at least) is that it can mostly be done 
[2], whoever I have found a bit intriguing that I need to 
explicitly use "this.i" instead of just "i" in B.fb() [3].

Just in case, the code I got to work is this:

class A {
	public static class I {
		public string fai() {
			return "A.I.fai";
	public string fa() {
		return i.fai();

	public this(this C)() {
		i_ = new C.I();
	protected I i_;
	public  property T.I i(this T)() { return cast(T.I) this.i_; }

class B : A {
	override public static class I : A.I {
		override public string fai() {
			return "B.I.fai";
		public string fbi() {
			return "B.I.fbi";
	public this(this C)() {
	public string fb() {
		return this.i.fbi(); // Why is "this" needed here?

void main() {
	A a = new A();
	A ab = new B();
	B b = new B();
	assert (a.fa() == "A.I.fai");
	assert (ab.fa() == "B.I.fai");
	assert (b.fa() == "B.I.fai");
	assert (b.fb() == "B.I.fbi");

Is there a reason for that? Why cannot it be inferred as in the 
regular case?

Also, if there's a way to do it without using the property 
wrapper, I'd be glad to know it :)

I tried something like:

template i(this T) {
     T.I i;
but it didn't like it... I guess members have to be better 



https://forum.dlang.org/thread/siwjqxiuocqtrldczand forum.dlang.org
[2]: https://dpaste.dzfl.pl/8f4e0df438e5
[3]: https://dpaste.dzfl.pl/8f4e0df438e5#line-34
Mar 24