tasks a-s

Task/Polymorphic-copy/D/polymorphic-copy-1.d

@@ -0,0 +1,19 @@
+class T {
+    override string toString() { return "I'm the instance of T"; }
+    T duplicate() { return new T; }
+}
+
+class S : T {
+    override string toString() { return "I'm the instance of S"; }
+
+    override T duplicate() { return new S; }
+}
+
+void main () {
+    import std.stdio;
+    T orig = new S;
+    T copy = orig.duplicate();
+
+    writeln(orig);
+    writeln(copy);
+}

Task/Polymorphic-copy/D/polymorphic-copy-2.d

@@ -0,0 +1,46 @@
+class T {
+    this(T t = null) {} // Constructor that will be used for copying.
+
+    override string toString() { return "I'm the instance of T"; }
+
+    T duplicate() { return new T(this); }
+
+    bool custom(char c) { return false; }
+}
+
+class S : T {
+    char[] str;
+
+    this(S s = null) {
+        super(s);
+        if (s is null)
+            str = ['1', '2', '3']; // All newly created will get that.
+        else
+            str = s.str.dup; // Do the deep-copy.
+    }
+
+    override string toString() {
+        return "I'm the instance of S p: " ~ cast(string)str;
+    }
+
+    override T duplicate() { return new S(this); }
+
+    // Additional procedure, just to test deep-copy.
+    override bool custom(char c) {
+        if (str !is null)
+            str[0] = c;
+        return str is null;
+    }
+}
+
+void main () {
+    import std.stdio;
+    T orig = new S;
+    orig.custom('X');
+
+    T copy = orig.duplicate();
+    orig.custom('Y');
+
+    writeln(orig);
+    writeln(copy); // Should have 'X' at the beginning.
+}