Ichthyostega
20392eee1c
This resolves an intricate problem related to metaprogramming with variadic templates and function signatures. Due to exceptional complexity, a direct solution was blocked for several years, and required a better organisation of the support code involved; several workarounds were developed, gradually leading to a transition path, which could now be completed in an focused clean-up effort over the last week. Metaprogramming with sequences of types is organised into three layers: - simple tasks can be solved with the standard facilities of the language, using pattern match with variadic template specialisations - the ''type-sequence'' construct `Types<T...>` takes the centre stage for the explicit definition of collections of types; it can be re-bound to other variadic templates and supports simple direct manipulation - for more elaborate and advanced processing tasks, a ''Loki-style type list'' can be obtained from a type-sequence, allowing to perform recursive list processing task with a technique similar to LISP.
153 lines
3.9 KiB
C++
153 lines
3.9 KiB
C++
/*
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VisitingTool(Test) - check the standard visitor use case
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Copyright (C)
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2008, Hermann Vosseler <Ichthyostega@web.de>
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**Lumiera** is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by the
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Free Software Foundation; either version 2 of the License, or (at your
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option) any later version. See the file COPYING for further details.
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* *****************************************************************/
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/** @file visitingtool-test.cpp
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** unit test \ref VisitingTool_test
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*/
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#include "lib/test/run.hpp"
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#include "lib/visitor.hpp"
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#include "lib/format-string.hpp"
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#include <iostream>
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using util::_Fmt;
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using std::string;
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using std::cout;
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namespace lib {
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namespace visitor {
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namespace test1 {
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typedef visitor::Tool<> VisitingTool;
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class HomoSapiens : public Visitable<>
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{
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public:
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DEFINE_PROCESSABLE_BY (VisitingTool);
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};
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class Boss : public HomoSapiens
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{
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public:
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DEFINE_PROCESSABLE_BY (VisitingTool);
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};
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class BigBoss : public Boss
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{
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public:
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DEFINE_PROCESSABLE_BY (VisitingTool);
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};
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class Visionary : public Boss
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{
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DEFINE_PROCESSABLE_BY (VisitingTool);
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};
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class Leader : public Visionary
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{
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/* can not be visited */
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};
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class VerboseVisitor
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: public VisitingTool
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{
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protected:
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void talk_to (string guy)
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{
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cout << _Fmt{"Hello %s, nice to meet you...\n"} % guy;
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}
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};
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class Babbler
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: public Applicable< Babbler
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, Types<Boss,BigBoss,Visionary>::List // dispatch calls to this types
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, VerboseVisitor // (base class / interface)
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>
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{
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public:
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void treat (Boss&) { talk_to("Boss"); }
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void treat (BigBoss&) { talk_to("Big Boss"); }
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};
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// note the following fine points:
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// - Babbler "forgot" to declare being applicable to HomoSapiens
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// - the class Leader hidden deep in the hierarchy is lacking an "apply()"-implementation
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/*********************************************************************//**
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* @test our lib implementation of the visitor pattern.
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* Defines a hierarchy of test classes to check the following cases
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* - calling the correct visiting tool specialised function
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* for given concrete hierarchy classes
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* - visiting tool not declaring to visit some class
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* is silently ignored by default
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* - newly added classes will be handled by existing
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* functions according to inheritance relations
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*/
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class VisitingTool_test : public Test
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{
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virtual void
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run (Arg)
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{
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known_visitor_known_class();
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visiting_extended_hierarchy();
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}
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void
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known_visitor_known_class()
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{
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Boss x1;
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BigBoss x2;
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// masquerade as HomoSapiens...
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HomoSapiens& homo1{x1};
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HomoSapiens& homo2{x2};
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cout << "=== Babbler meets Boss and BigBoss ===\n";
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Babbler bab;
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VisitingTool& vista{bab};
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homo1.apply (vista);
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homo2.apply (vista);
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}
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void
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visiting_extended_hierarchy()
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{
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HomoSapiens x1;
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Leader x2;
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HomoSapiens& homo1 (x1);
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HomoSapiens& homo2 (x2);
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cout << "=== Babbler meets HomoSapiens and Leader ===\n";
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Babbler bab;
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VisitingTool& vista (bab);
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homo1.apply (vista); // silent error handler (not Applicable to HomoSapiens)
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homo2.apply (vista); // Leader handled as Visionary and treated as Boss
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}
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};
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/** Register this test class... */
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LAUNCHER (VisitingTool_test, "unit common");
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}}} // namespace lib::visitor::test1
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