Ichthyostega
4caf790339
- move construct into the buffer - directly invoke the payload constructor through PlantingHandle - reconsider type signature and size constraint - extend the unit test - document a corner case of c++ "perfect forwarding", which caused me some grief here
484 lines
16 KiB
C++
484 lines
16 KiB
C++
/*
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SCOPED-COLLECTION.hpp - managing a fixed collection of noncopyable polymorphic objects
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Copyright (C) Lumiera.org
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2012, 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 scoped-collection.hpp
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** Managing a collection of non-copyable polymorphic objects in compact storage.
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** This helper supports the frequently encountered situation where a service
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** implementation internally manages a collection of implementation related
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** sub-components with reference semantics. Typically, those objects are
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** being used polymorphically, and often they are also added step by step.
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** The storage holding all those child objects is allocated in one chunk
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** and never adjusted.
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**
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** # usage patterns
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**
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** The common ground for all usage of this container is to hold some elements
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** with exclusive ownership; when the enclosing container goes out of scope,
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** all the dtors of the embedded objects will be invoked. Frequently this
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** side effect is the reason for using the container: we want to own some
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** resource handles to be available exactly as long as the managing object
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** needs and accesses them.
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**
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** There are two different usage patterns for populating a ScopedCollection
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** - the "stack style" usage creates an empty container (using the one arg
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** ctor just to specify the maximum size). The storage to hold up to this
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** number of objects is (heap) allocated right away, but no objects are
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** created. Later on, individual objects are "pushed" into the collection
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** by invoking #emplaceElement() to create a new element of the default
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** type `I`) or #emplace<Type>(args) to create some subtype. This way,
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** the container is being filled successively.
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** - the "RAII style" usage strives to create all of the content objects
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** right away, immediately after the memory allocation. This usage pattern
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** avoids any kind of "lifecycle state". Either the container comes up sane
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** and fully populated, or the ctor call fails and any already created
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** objects are discarded.
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** @note intentionally there is no operation to discard individual objects,
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** all you can do is to #clear() the whole container.
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** @note the container can hold instances of a subclass of the type defined
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** by the template parameter `I`. But you need to ensure in this case
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** that the defined buffer size for each element (2nt template parameter)
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** is sufficient to hold any of these subclass instances. This condition
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** is protected by a static assertion (compilation failure).
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** @warning when using subclasses, a virtual dtor is mandatory
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** @warning deliberately \em not threadsafe
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**
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** @see ScopedCollection_test
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** @see scoped-ptrvect.hpp quite similar, but using individual heap pointers
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*/
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#ifndef LIB_SCOPED_COLLECTION_H
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#define LIB_SCOPED_COLLECTION_H
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#include "lib/error.hpp"
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#include "lib/nocopy.hpp"
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#include "lib/meta/trait.hpp"
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#include "lib/iter-adapter.hpp"
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#include <type_traits>
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namespace lib {
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namespace error = lumiera::error;
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using error::LERR_(CAPACITY);
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using error::LERR_(INDEX_BOUNDS);
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/**
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* A fixed collection of non-copyable polymorphic objects.
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*
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* All child objects reside in a common chunk of storage
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* and are owned and managed by this collection holder.
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* Array style access and iteration is provided.
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* @tparam I the nominal Base/Interface class for a family of types
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* @tparam siz maximum storage required for the targets to be held inline
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*/
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template
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< class I
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, size_t siz = sizeof(I)
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>
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class ScopedCollection
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: util::NonCopyable
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{
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public:
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/**
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* Storage Frame to hold one Child object.
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* The storage will be an heap allocated
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* array of such Wrapper objects.
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* @note doesn't manage the Child
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*/
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class ElementHolder
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: util::NonCopyable
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{
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mutable char buf_[siz];
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public:
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I&
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accessObj() const
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{
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return reinterpret_cast<I&> (buf_);
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}
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void
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destroy()
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{
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accessObj().~I();
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}
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/** place object of type TY, forwarding ctor arguments */
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template<class TY, typename...ARGS>
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TY&
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create (ARGS&& ...args)
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{
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static_assert ( meta::is_Subclass<TY,I>()
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&& sizeof(TY) <= siz,
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"ElementHolder buffer too small");
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return *new(&buf_) TY (std::forward<ARGS> (args)...);
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}
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};
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~ScopedCollection ()
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{
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clear();
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}
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explicit
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ScopedCollection (size_t maxElements)
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: level_(0)
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, capacity_(maxElements)
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, elements_(new ElementHolder[maxElements])
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{ }
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/** creating a ScopedCollection in RAII-style:
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* The embedded elements will be created immediately.
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* Ctor fails in case of any error during element creation.
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* @param builder functor to be invoked for each "slot".
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* It gets an ElementHolder& as parameter, and should
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* use this to create an object of some I-subclass
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*/
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template<class CTOR>
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ScopedCollection (size_t maxElements, CTOR builder)
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: level_(0)
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, capacity_(maxElements)
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, elements_(new ElementHolder[maxElements])
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{
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populate_by (builder);
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}
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/** variation of RAII-style: using a builder function,
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* which is a member of some object. This supports the
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* typical usage situation, where a manager object builds
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* a ScopedCollection of some components
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* @param builder member function used to create the elements
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* @param instance the owning class instance, on which the
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* builder member function will be invoked ("this").
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*/
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template<class TY>
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ScopedCollection (size_t maxElements, void (TY::*builder) (ElementHolder&), TY * const instance)
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: level_(0)
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, capacity_(maxElements)
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, elements_(new ElementHolder[maxElements])
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{
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populate_by (builder,instance);
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}
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/* == some pre-defined Builders == */
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class FillAll; ///< fills the ScopedCollection with default constructed I-instances
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template<typename TY>
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class FillWith; ///< fills the ScopedCollection with default constructed TY-instances
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template<typename IT>
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class PullFrom; ///< fills by copy-constructing values pulled from the iterator IT
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template<typename IT>
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static PullFrom<IT>
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pull (IT iter) ///< convenience shortcut to pull from any given Lumiera Forward Iterator
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{
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return PullFrom<IT> (iter);
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}
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void
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clear()
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{
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REQUIRE (level_ <= capacity_, "Storage corrupted");
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while (level_)
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{
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--level_;
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try {
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elements_[level_].destroy();
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}
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ERROR_LOG_AND_IGNORE (progress, "Clean-up of element in ScopedCollection")
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}
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}
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/** init all elements default constructed */
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void
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populate()
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try {
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while (level_ < capacity_)
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{
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elements_[level_].template create<I>();
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++level_;
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}
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}
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catch(...)
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{
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WARN (progress, "Failure while populating ScopedCollection. "
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"All elements will be discarded");
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clear();
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throw;
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}
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/** init all elements at once,
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* invoking a builder functor for each.
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* @param builder to create the individual elements
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* this functor is responsible to invoke the appropriate
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* ElementHolder#create function, which places a new element
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* into the storage frame passed as parameter.
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*/
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template<class CTOR>
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void
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populate_by (CTOR builder)
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try {
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while (level_ < capacity_)
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{
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ElementHolder& storageFrame (elements_[level_]);
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builder (storageFrame);
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++level_;
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} }
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catch(...)
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{
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WARN (progress, "Failure while populating ScopedCollection. "
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"All elements will be discarded");
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clear();
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throw;
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}
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/** variation of element initialisation,
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* invoking a member function of some manager object
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* for each collection element to be created.
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*/
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template<class TY>
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void
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populate_by (void (TY::*builder) (ElementHolder&), TY * const instance)
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try {
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while (level_ < capacity_)
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{
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ElementHolder& storageFrame (elements_[level_]);
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(instance->*builder) (storageFrame);
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++level_;
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} }
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catch(...)
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{
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WARN (progress, "Failure while populating ScopedCollection. "
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"All elements will be discarded");
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clear();
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throw;
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}
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/** push a new element of default type
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* to the end of this container
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* @note EX_STRONG */
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I&
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emplaceElement()
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{
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return emplace<I>();
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}
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/**
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* push new entry at the end of this container
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* and build object of type TY in place there
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*/
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template<class TY, typename...ARGS>
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TY&
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emplace (ARGS&& ...args)
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{
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__ensureSufficientCapacity();
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TY& newElm = elements_[level_].template create<TY>(std::forward<ARGS> (args)...);
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++level_;
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return newElm;
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}
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/* === Element access and iteration === */
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I&
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operator[] (size_t index) const
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{
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if (index < level_)
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return elements_[index].accessObj();
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throw error::Logic ("Attempt to access not (yet) existing object in ScopedCollection"
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, LERR_(INDEX_BOUNDS));
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}
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using iterator = IterAdapter< I *, const ScopedCollection *>;
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using const_iterator = IterAdapter<const I *, const ScopedCollection *>;
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iterator begin() { return iterator (this, _access_begin()); }
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const_iterator begin() const { return const_iterator (this, _access_begin()); }
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iterator end () { return iterator(); }
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const_iterator end () const { return const_iterator(); }
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size_t size () const { return level_; }
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size_t capacity () const { return capacity_; }
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bool empty () const { return 0 == level_; }
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private:
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/* ==== Storage: heap allocated array of element buffers ==== */
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typedef std::unique_ptr<ElementHolder[]> ElementStorage;
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size_t level_;
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size_t capacity_;
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ElementStorage elements_;
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void
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__ensureSufficientCapacity()
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{
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if (level_ >= capacity_)
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throw error::State ("ScopedCollection exceeding the initially defined capacity"
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, LERR_(CAPACITY));
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}
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/* ==== internal callback API for the iterator ==== */
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/** Iteration-logic: switch to next position
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* @note assuming here that the start address of the embedded object
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* coincides with the start of an array element (ElementHolder)
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*/
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friend void
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iterNext (const ScopedCollection*, I* & pos)
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{
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ElementHolder* & storageLocation = reinterpret_cast<ElementHolder* &> (pos);
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++storageLocation;
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}
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friend void
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iterNext (const ScopedCollection*, const I* & pos)
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{
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const ElementHolder* & storageLocation = reinterpret_cast<const ElementHolder* &> (pos);
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++storageLocation;
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}
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/** Iteration-logic: detect iteration end. */
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template<typename POS>
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friend bool
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checkPoint (const ScopedCollection* src, POS & pos)
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{
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REQUIRE (src);
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if ((pos) && (pos < src->_access_end()))
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return true;
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else
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{
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pos = 0;
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return false;
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} }
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I* _access_begin() const { return & elements_[0].accessObj(); }
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I* _access_end() const { return & elements_[level_].accessObj(); }
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};
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/* === Supplement: pre-defined element builders === */
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/** \par usage
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* Pass an instance of this builder functor as 2nd parameter
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* to ScopedCollections's ctor. (an anonymous instance is OK).
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* Using this variant of the ctor switches the collection to RAII-style:
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* It will immediately try to create all the embedded objects, invoking this
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* builder functor for each "slot" to hold such an embedded object. Actually,
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* this "slot" is an ElementHolder instance, which provides functions for
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* placement-creating objects into this embedded buffer.
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*/
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template<class I, size_t siz>
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class ScopedCollection<I,siz>::FillAll
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{
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public:
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void
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operator() (typename ScopedCollection<I,siz>::ElementHolder& storage)
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{
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storage.template create<I>();
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}
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};
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template<class I, size_t siz>
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template<typename TY>
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class ScopedCollection<I,siz>::FillWith
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{
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public:
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void
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operator() (typename ScopedCollection<I,siz>::ElementHolder& storage)
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{
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storage.template create<TY>();
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}
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};
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/** \par usage
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* This variant allows to "pull" elements from an iterator.
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* Actually, the collection will try to create each element right away,
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* by invoking the copy ctor and passing the value yielded by the iterator.
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* @note anything in accordance to the Lumera Forward Iterator pattern is OK.
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* This rules out just passing a plain STL iterator (because these can't
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* tell for themselves when they're exhausted). Use an suitable iter-adapter
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* instead, e.g. by invoking lib::iter_stl::eachElm(stl_container)
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*/
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template<class I, size_t siz>
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template<typename IT>
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class ScopedCollection<I,siz>::PullFrom
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{
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IT iter_;
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typedef typename meta::TypeBinding<IT>::value_type ElementType;
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public:
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PullFrom (IT source)
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: iter_(source)
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{ }
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void
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operator() (typename ScopedCollection<I,siz>::ElementHolder& storage)
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{
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storage.template create<ElementType> (*iter_);
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++iter_;
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}
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};
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} // namespace lib
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#endif
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