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--- at:tutorial:appendix [2008/07/10 16:24] – * tvcutsem
+++ at:tutorial:appendix [2008/07/10 16:31] – added tvcutsem
@@ Line 505: / Line 505: @@
 ==== Structural Types ====
+The module ''/.at.lang.structuraltypes'' implements a small library to use structural typing. The library allows for the creation of 'protocols', which are first-class structural types. A structural type is simply a set of selectors. An object o conforms to a protocol P <=> for all selectors s of P, o respondsTo s where respondsTo is determined by o's mirror.
+A structural type can be branded with type tags. In this case, objects only conform to the type if they are structurally conformant **and** if they are tagged with the structural type's brands.
+Use the ''protocol:'' function to create a new protocol:
+<code>
+def PersonProtocol := protocol: {
+  def name;
+  def age;
+} named: `Person;
+</code>
+The ''`Person'' argument is used to give the protocol a name simply for display purposes. The ''object:implements:'' function automatically checks whether an object conforms to any declared types:
+<code>
+def tom := object: {
+  def name := "Tom";
+  def age() { 24 };
+} implements: PersonProtocol;
+</code>
+You can also create a protocol from an object:
+<code>def tomsProtocol := protocolOf: tom;</code>
+You can test protocol conformance in either of two styles:
+  * ''does: tom implement: PersonProtocol'' => true or false
+  * ''PersonProtocol <? tom'' => true or false
+You can also force a ''StructuralTypeMismatch'' exception to be raised if the object does not conform to the type:
+ *  ''ensure: tom implements: PersonProtocol'' => true or exception
+ *  ''PersonProtocol.checkConformance(tom)'' => true or exception
+More usage examples of structural types can be found in the unit test defined in the file ''at/lang/structuraltypes.at''.
 ==== Traits ====