Ichthyostega
bc6a219543
Now looking into largely obsolete library facilities... Starting from `ScopedHolder`, I found a surprising problem with ''perfect forwarding....'' ...which however turned out to be the result of ''sloppy programming'' on my side. At that time, in 2017, seemingly I was under pressure to define a Session-Command, which captures a Time-entity as »State Memento«. Which turned out to be impossible, since the Time entities were conceived as being immutable -- a questionable design decision (see #1261), which already generated quite some additional complexities. In the course of this »exercise«, I could again clarify that the implementation of perfect forwarding works as expected on modern compilers — confusion may arrise sometimes due to ''copy elision'' (which the compiler is required to perform since C++17, even when the elided constructor has observable side effects). And it can be derailed when (as was the case here) a »grab everything« constructor accidentally ends up generating a copy- or move-constructor for the container class itself. This is an instance of the problem documented with #963 ... .... and the best solution is to abide by the rule-of-five (and a half) and to put that `ReplacableItem` to where it belongs...
128 lines
3.7 KiB
C++
128 lines
3.7 KiB
C++
/*
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MementoTie(Test) - check the mechanism for capturing and providing undo-state
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Copyright (C)
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2009, 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 memento-tie-test.cpp
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** unit test \ref MementoTie_test
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*/
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#include "lib/test/run.hpp"
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#include "lib/test/test-helper.hpp"
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#include "steam/control/memento-tie.hpp"
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#include <functional>
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using std::function;
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using std::bind;
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namespace steam {
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namespace control {
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namespace test {
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namespace {
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int testVal=0; ///< used to verify the effect of testFunc
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void
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undo (short param, int memento) ///< simulates "Undo" of the command operation
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{
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testVal += param-memento;
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}
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int
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capture (short param) ///< simulates capturing the undo state
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{
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return testVal+param;
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}
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/** maximum additional storage maybe wasted due
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* to alignment of the memento value within MementoTie
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*/
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const size_t ALIGNMENT = sizeof(size_t);
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}
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using LERR_(MISSING_MEMENTO);
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/*************************************************************************************//**
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* @test Verify the state capturing mechanism (memento), which is used to implement
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* the Undo() functionality for Steam-Layer commands. Bind an undo function and a state
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* capturing function and wire up both to store and retrieve a memento value.
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* Verify that after closing the functions, actually state is captured by each invocation.
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*
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* @see control::Command
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* @see control::CmdClosure
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* @see control::UndoMutation
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* @see command-mutation-test.hpp
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*/
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class MementoTie_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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seedRand();
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checkStateCapturingMechanism();
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}
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/// assumed signature of the Command "Operation"
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typedef void OpSIG(short);
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typedef MementoTie<OpSIG,int> MemHolder;
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void
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checkStateCapturingMechanism ()
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{
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function<void(short,int)> undo_func = undo;
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function< int(short)> cap_func = capture;
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MemHolder mementoHolder (undo_func,cap_func);
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function<OpSIG> bound_undo_func = mementoHolder.tieUndoFunc();
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function<OpSIG> bound_cap_func = mementoHolder.tieCaptureFunc();
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VERIFY_ERROR (MISSING_MEMENTO, bound_undo_func(123) );
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VERIFY_ERROR (MISSING_MEMENTO, mementoHolder.getState() );
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short rr (rani (100));
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testVal = 0;
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bound_cap_func(rr); // invoke state capturing
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CHECK (rr == mementoHolder.getState());
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testVal = 10; // meanwhile "somehow" mutate the state
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bound_undo_func(0); // invoking the undo() feeds back the memento
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CHECK (testVal == 10-rr);
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// this cycle can be repeated with different state values
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rr = rani (100);
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testVal = rr;
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bound_cap_func(5); // capture new state
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CHECK (5+rr == mementoHolder.getState());
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testVal = -20;
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bound_undo_func(3*rr);
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CHECK (testVal == -20 + 3*rr - (5+rr));
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}
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};
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/** Register this test class... */
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LAUNCHER (MementoTie_test, "unit controller");
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}}} // namespace steam::control::test
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