Ichthyostega
a90b9e5f16
In the Lumiera code base, we use C-String constants as unique error-IDs. Basically this allows to create new unique error IDs anywhere in the code. However, definition of such IDs in arbitrary namespaces tends to create slight confusion and ambiguities, while maintaining the proper use statements requires some manual work. Thus I introduce a new **standard scheme** * Error-IDs for widespread use shall be defined _exclusively_ into `namespace lumiera::error` * The shorthand-Macro `LERR_()` can now be used to simplify inclusion and referral * (for local or single-usage errors, a local or even hidden definition is OK)
160 lines
3.8 KiB
C++
160 lines
3.8 KiB
C++
/*
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OPTIONAL-REF.hpp - optional and switchable reference
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Copyright (C) Lumiera.org
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2010, 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 optional-ref.hpp
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** a checked, switchable reference.
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** Offers semantics similar to a pointer, but throws (not segfaults)
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** on invalid dereferentiation
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*/
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#ifndef LIB_OPTIONAL_REF_H
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#define LIB_OPTIONAL_REF_H
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#include "lib/error.hpp"
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namespace lib {
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using LERR_(BOTTOM_VALUE);
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/**
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* Optional or switchable link to an existing object.
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* This reference wrapper is accessed like a functor,
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* but has the ability to be \em disabled. This disabled state
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* is managed automatically by ctor and dtor, can be detected
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* through \c bool check and -- contrary to a \c NULL pointer
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* -- produces a real exception instead of crashing.
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*
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* @note \em not taking ownership of the pointee
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*
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* @see OptionalRef_test
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* @see lib::AutoRegistered usage example
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* @see SessionInterfaceModules::~SessionInterfaceModules()
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*
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*/
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template<typename T>
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class OptionalRef
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{
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T* ref_;
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public:
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OptionalRef()
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: ref_(0)
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{ }
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~OptionalRef()
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{
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clear();
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}
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// using default copy operations...
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explicit
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OptionalRef(T& target) ///< ...\em not allowing implicit conversion from T&
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: ref_(&target)
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{ }
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explicit operator bool() const { return isValid(); }
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T&
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operator() () const
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{
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if (!isValid())
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throw lumiera::error::Logic ("access to this object is (not/yet) enabled"
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, LERR_(BOTTOM_VALUE));
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return *ref_;
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}
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/* === mutations ===*/
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void
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link_to (T& target)
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{
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ref_ = ⌖
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}
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void
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clear()
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{
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ref_ = 0;
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}
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/* === comparison and diagnostics === */
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bool
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isValid() const
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{
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return bool(ref_);
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}
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bool
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points_to (T const& target) const
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{
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return isValid()
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&& ref_ == ⌖
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}
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friend bool
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operator== (OptionalRef const& r1, OptionalRef const& r2)
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{
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return r1.ref_ == r2.ref_;
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}
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friend bool
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operator!= (OptionalRef const& r1, OptionalRef const& r2)
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{
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return r1.ref_ != r2.ref_;
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}
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// mixed comparisons
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friend bool
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operator== (OptionalRef const& ref, T const& otherTarget) ///< @note might throw
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{
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return ref() == otherTarget;
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}
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friend bool operator== (T const& otherTarget, OptionalRef const& ref) { return ref == otherTarget; }
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friend bool operator!= (T const& otherTarget, OptionalRef const& ref) { return !(ref == otherTarget); }
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friend bool operator!= (OptionalRef const& ref, T const& otherTarget) { return !(ref == otherTarget); }
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};
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template<typename T>
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OptionalRef<T>
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optionalRefTo (T& target)
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{
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return OptionalRef<T> (target);
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}
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} // namespace lib
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#endif
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