Calls `this(this)` extra with delegate stuff in the code

[Joel via Digitalmars-d-learn]

Compile this and see, (it's crazy!):

import std.stdio;

struct Widget {
        private int[] array;
        this(uint length) {
                array = new int[length];
        }
        this(this) {
                writeln( "this(this) called" );
                array = array.dup;
        }
        int get(size_t offset) { return array[offset]; }
        void set(size_t offset, int value) { array[offset] = value; }
        auto getArray() {
                return array;
        }
}

void main() {
        auto w1 = Widget(10);
        auto w2 = Widget(10);
        w1.set(5, 100);
        w2.set(5, 42);
        assert(w1.get(5) == 100);
        
        auto wd1 = Widget(3);
        Widget wd2 = Widget(3);
        wd1.set(0, 1);
        wd1.set(1, 2);
        wd1.set(2, 3);
        assert( wd1.getArray == [1,2,3] );
        assert( wd2.getArray == [0,0,0] );
        void update(string message) {
                writeln(message, " wd1 = ", wd1, ", wd2 = ", wd2);
        }
        void delegate(string) print = &update;
        print("before");
        wd2 = wd1;
        print("after");

        assert( wd2.getArray == [1,2,3] );
}