Initial data commit

Task/Empty-string/D/empty-string.d

@@ -0,0 +1,27 @@
+import std.array;
+
+bool isEmptyNotNull(in string s) pure nothrow @safe {
+    return s is "";
+}
+
+void main(){
+    string s1 = null;
+    string s2 = "";
+
+    // the content is the same
+    assert(!s1.length);
+    assert(!s2.length);
+    assert(s1 == "" && s1 == null);
+    assert(s2 == "" && s2 == null);
+    assert(s1 == s2);
+
+    // but they don't point to the same memory region
+    assert(s1 is null && s1 !is "");
+    assert(s2 is "" && s2 !is null);
+    assert(s1 !is s2);
+    assert(s1.ptr == null);
+    assert(*s2.ptr == '\0'); // D string literals are \0 terminated
+
+    assert(s1.empty);
+    assert(s2.isEmptyNotNull());
+}