Ichthyostega
e81b0592d3
...and complete unit test coverage. This is complex stuff and we'd better be careful it actually works
124 lines
4.7 KiB
C++
124 lines
4.7 KiB
C++
/*
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TREE-MUTATOR-NOOP-BINDING.hpp - diff::TreeMutator implementation building block
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Copyright (C) Lumiera.org
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2018, Hermann Vosseler <Ichthyostega@web.de>
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License as
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published by the Free Software Foundation; either version 2 of
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the License, or (at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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/** @file tree-mutator-noop-binding.hpp
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** Special binding implementation for TreeMutator, allowing to accept
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** and ignore any tree diff without tangible effect. TreeMutator is a
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** customisable intermediary, which enables otherwise opaque implementation
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** data structures to receive and respond to generic structural change messages
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** ("tree diff").
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**
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** Each concrete TreeMutator instance will be configured differently, and this
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** adaptation is done by combining various building blocks. This header defines
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** a special `/dev/null` building block, which behaves as if successfully consuming
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** the given diff without actually doing anything. Obviously, such a "black hole layer"
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** need to be below any other diff binding, and may be used to absorb any diff verbs
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** not matched and consumed by a more specific binding. Contrast this to the TreeMutator
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** default implementation, which likewise absorbs diff verbs, but in a way to trigger
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** a lumiera::error::LUMIERA_ERROR_DIFF_CONFLICT.
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**
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** @note the header tree-mutator-attribute-binding.hpp was split off for sake of readability
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** and is included automatically from bottom of tree-mutator.hpp
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**
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** @see tree-mutator-test.cpp
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** @see TreeMutator::build()
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**
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*/
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#ifndef LIB_DIFF_TREE_MUTATOR_NOOP_BINDING_H
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#define LIB_DIFF_TREE_MUTATOR_NOOP_BINDING_H
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#include "lib/error.hpp"
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#include "lib/diff/gen-node.hpp"
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#include "lib/diff/tree-mutator.hpp"
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#include <type_traits>
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namespace lib {
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namespace diff{
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namespace { // Mutator-Builder decorator components...
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/**
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* Diff binding for black holes, happily accepting anything.
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* @note absorbs and silently ignores any diff verb.
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*/
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class BlackHoleMutation
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: public TreeMutator
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{
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public:
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BlackHoleMutation () = default;
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/* ==== TreeMutator API ==== */
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using Elm = GenNode const&;
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using Buff = TreeMutator::Handle;
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bool hasSrc() override { return true; } ///< always keen to do yet more
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bool injectNew (Elm) override { return true; } ///< pretend to inject something new
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bool matchSrc (Elm) override { return true; } ///< purport suitable element is waiting
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bool acceptSrc (Elm) override { return true; } ///< claim to handle any diff task
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bool accept_until (Elm) override { return true; } ///< profess to forward anywhere
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bool findSrc (Elm) override { return true; } ///< sham to find anything
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bool assignElm (Elm) override { return true; } ///< accept any assignment
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bool
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mutateChild (Elm, Buff buff) override ///< ignore inferiors, yet reproduce yourself
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{
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buff.create (BlackHoleMutation());
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return true;
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}
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};
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/** Entry point for DSL builder: create a binding which consumes any diff without effect.
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* @warning must be used as bottom most layer in a custom TreeMutator, since it would
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* otherwise shadow and disable any binding layer below.
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* @note however it is possible to add a (typically selective) binding layer on top;
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* any diff verb _not handled_ by such a top layer will fall through and
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* be silently ignored. Such a setup can be used to "fish" for some specific
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* attributes within a diff stream.
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*/
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template<class PAR>
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inline auto
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Builder<PAR>::ignoreAllChanges()
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{
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static_assert (std::is_same<PAR, TreeMutator>()
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,"ignoreAllChanges() must be used as bottom layer.");
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return Builder<BlackHoleMutation> (BlackHoleMutation{});
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}
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}//(END)Mutator-Builder decorator components...
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}} // namespace lib::diff
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#endif /*LIB_DIFF_TREE_MUTATOR_NOOP_BINDING_H*/
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