StoreGate/StoreGate/ReadDecorHandle.icc

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/*
 * Copyright (C) 2002-2025 CERN for the benefit of the ATLAS collaboration.
 */
/**
 * @file StoreGate/ReadDecorHandle.icc
 * @author scott snyder <snyder@bnl.gov>
 * @date Apr, 2017
 * @brief Handle class for reading a decoration on an object.
 */
 
 
namespace SG {
 
 
/**
 * @brief Constructor from a ReadDecorHandleKey.
 * @param key The key object holding the clid/key/store/attr.
 *
 * This will raise an exception if the StoreGate key is blank,
 * or if the event store cannot be found.
 */
template <class T, class D>
ReadDecorHandle<T, D>::ReadDecorHandle (const ReadDecorHandleKey<T>& key)
  : Base (key.contHandleKey()),
    m_decorKey (key.key()),
    m_acc (SG::decorKeyFromKey (key.key()))
{
}
 
 
/**
 * @brief Constructor from a ReadDecorHandleKey and an explicit event context.
 * @param key The key object holding the clid/key.
 * @param ctx The event context.
 *
 * This will raise an exception if the StoreGate key is blank,
 * or if the event store cannot be found.
 *
 * If the default event store has been requested, then the thread-specific
 * store from the event context will be used.
 */
template <class T, class D>
ReadDecorHandle<T, D>::ReadDecorHandle (const ReadDecorHandleKey<T>& key,
                                        const EventContext& ctx)
  : Base (key.contHandleKey(), ctx),
    m_decorKey (key.key()),
    m_acc (SG::decorKeyFromKey (key.key()))
{
}
 
 
/**
 * @brief Copy constructor.
 */
template <class T, class D>
ReadDecorHandle<T, D>::ReadDecorHandle (const ReadDecorHandle& rhs)
  : Base (rhs),
    m_decorKey (rhs.m_decorKey),
    m_acc (rhs.m_acc)
{
}
 
 
/**
 * @brief Move constructor.
 */
template <class T, class D>
ReadDecorHandle<T, D>::ReadDecorHandle (ReadDecorHandle&& rhs)
  : Base (std::move (rhs)),
    m_decorKey (std::move (rhs.m_decorKey)),
    m_acc (std::move (rhs.m_acc))
{
}
 
 
/**
 * @brief Assignment operator.
 */
template <class T, class D>
ReadDecorHandle<T, D>& ReadDecorHandle<T, D>::operator= (const ReadDecorHandle& rhs)
{
  if (this != &rhs) {
    *static_cast<Base*>(this) = rhs;
    m_decorKey = rhs.m_decorKey;
    m_acc = rhs.m_acc;
  }
  return *this;
}
 
 
/**
 * @brief Move operator.
 */
template <class T, class D>
ReadDecorHandle<T, D>& ReadDecorHandle<T, D>::operator= (ReadDecorHandle&& rhs)
{
  if (this != &rhs) {
    *static_cast<Base*>(this) = std::move (rhs);
    m_decorKey = std::move (rhs.m_decorKey);
    m_acc = std::move (rhs.m_acc);
  }
  return *this;
}
 
 
/**
 * @brief Is the referenced container present in SG?
 *
 * Note that this tests for the presence of the _container_,
 * not for the decoration.
 *
 * Const method; the handle does not change as a result of this.
 */
template <class T, class D>
inline
bool ReadDecorHandle<T, D>::isPresent() const
{
  return Base::isPresent();
}
 
 
/**
 * @brief Fetch the variable for one element, as a const reference.
 * @param e The element for which to fetch the variable.
 */
template <class T, class D>
inline
typename ReadDecorHandle<T, D>::const_reference_type
ReadDecorHandle<T, D>::operator() (const AuxElement& e) const
{
  // FIXME?  In principle, should check here that E is actually an element
  // of our declared container.  But that would force a SG lookup here
  // which we otherwise wouldn't need to do.
  return m_acc (e);
}
 
 
/**
 * @brief Fetch the variable for one element, as a const reference.
 * @param index The index of the desired element.
 *
 * This looks up the variable in the object referenced by this handle.
 * For a standalone object, pass an index of 0.
 */
template <class T, class D>
inline
typename ReadDecorHandle<T, D>::const_reference_type
ReadDecorHandle<T, D>::operator() (size_t i)
{
  return m_acc (*this->vectorData(), i);
}
 
 
/**
 * @brief Fetch the variable for one element, as a const reference.
 * @param e The element for which to fetch the variable.
 * @param deflt Default value.
 *
 * If this variable is not available, then return @c deflt instead.
 */
template <class T, class D>
inline
typename ReadDecorHandle<T, D>::const_reference_type
ReadDecorHandle<T, D>::withDefault (const AuxElement& e, const D& deflt) const
{
  // FIXME?  In principle, should check here that E is actually an element
  // of our declared container.  But that would force a SG lookup here
  // which we otherwise wouldn't need to do.
  return m_acc.withDefault (e, deflt);
}
 
 
/**
 * @brief Fetch the variable for one element, as a const reference.
 * @param index The index of the desired element.
 * @param deflt Default value.
 *
 * This looks up the variable in the object referenced by this handle.
 * For a standalone object, pass an index of 0.
 * If this variable is not available, then return @c deflt instead.
 */
template <class T, class D>
inline
typename ReadDecorHandle<T, D>::const_reference_type
ReadDecorHandle<T, D>::withDefault (size_t i, const D& deflt)
{
  return m_acc.withDefault (*this->vectorData(), i, deflt);
}
 
 
/**
 * @brief Get a pointer to the start of the auxiliary data array.
 *        for the referenced object.
 */
template <class T, class D>
template <class POINTER_TYPE /*= const_container_pointer_type*/>
requires (!std::is_void_v<POINTER_TYPE>)
POINTER_TYPE
ReadDecorHandle<T, D>::getDataArray()
{
  return m_acc.getDataArray (*this->vectorData());
}
 
 
/**
 * @brief Get a span over the auxilary data array,
 *        for the referenced object.
 */
template <class T, class D>
auto
ReadDecorHandle<T, D>::getDataSpan() -> const_span
{
  return m_acc.getDataSpan (*this->vectorData());
}
 
 
/**
 * @brief Test to see if this variable exists in the store,
 *        for the referenced object.
 */
template <class T, class D>
inline
bool ReadDecorHandle<T, D>::isAvailable()
{
  const SG::AuxVectorData* vec = this->vectorData();
  return vec && vec->isAvailable (m_acc.auxid());
}
 
 
/**
 * @brief Return the aux id for this variable.
 */
template <class T, class D>
inline
SG::auxid_t ReadDecorHandle<T, D>::auxid() const
{
  return m_acc.auxid();
}
 
 
/**
 * @brief Return the name of the decoration alias (CONT.DECOR).
 */
template <class T, class D>
inline
const std::string& ReadDecorHandle<T, D>::decorKey() const
{
  return m_decorKey;
}
 
 
/** 
 * @brief Return the referenced object as a @c SG::AuxVectorData.
 *        Specialization for the case of a standalone object
 *        (@c T derives from @c SG::AuxElement).
 */
template <class T, class D>
inline
const SG::AuxVectorData* ReadDecorHandle<T, D>::vectorData (std::true_type)
{
  return (*this)->container();
}
 
 
/** 
 * @brief Return the referenced object as a @c SG::AuxVectorData.
 *        Specialization for the case of a container
 *        (@c T does not derive from @c SG::AuxElement).
 */
template <class T, class D>
inline
const SG::AuxVectorData* ReadDecorHandle<T, D>::vectorData (std::false_type)
{
  return this->cptr();
}
 
 
/** 
 * @brief Return the referenced object as a @c SG::AuxVectorData.
 *
 * If @c T is a container object, then this should be the object itself.
 * But if it is a standalone object, deriving from @c SG::AuxElement,
 * then we need to call container() on the object.
 */
template <class T, class D>
inline
const SG::AuxVectorData* ReadDecorHandle<T, D>::vectorData()
{
  // Dispatch to the appropriate specialization, depending on whether or not
  // @c T derives from @c SG::AuxElement.
  return vectorData (typename std::is_base_of<SG::AuxElement, T>::type());
}
 
 
/**
 * @brief Return a @c ReadDecorHandle referencing @c key.
 * @param key The key object holding the clid/key/store.
 *
 * This will raise an exception if the StoreGate key is blank,
 * or if the event store cannot be found.
 *
 * The type of the decoration must be included as an explicit template parameter:
 *
 *@code
 *   auto handle = SG::makeHandle<float> (key);
 @endcode
 *
 * Note that @c D comes first in the argument list.  It's given explicitly,
 * while @c T is inferred from @c key.
 */
template <class D, class T>
ReadDecorHandle<T, D> makeHandle (const ReadDecorHandleKey<T>& key)
{
  return ReadDecorHandle<T, D> (key);
}
 
 
/**
 * @brief Return a @c ReadDecorHandle referencing @c key for an explicit context.
 * @param key The key object holding the clid/key/store.
 * @param ctx The event context.
 *
 * This will raise an exception if the StoreGate key is blank,
 * or if the event store cannot be found.
 *
 * If the default event store has been requested, then the thread-specific
 * store from the event context will be used.
 *
 * The type of the decoration must be included as an explicit template parameter:
 *
 *@code
 *   auto handle = SG::makeHandle<float> (key, ctx);
 @endcode
 *
 * Note that @c D comes first in the argument list.  It's given explicitly,
 * while @c T is inferred from @c key.
 */
template <class D, class T>
ReadDecorHandle<T, D> makeHandle (const ReadDecorHandleKey<T>& key,
                                  const EventContext& ctx)
{
  return ReadDecorHandle<T, D> (key, ctx);
}
 
 
/**
 * @brief These two signatures are to catch cases where the explicit
 *        template argument is omitted from the @c makeHandle call
 *        and give an error tailored to that.  Otherwise, the @c makeHandle
 *        call for @c ReadHandle would match, potentially giving a much
 *        more confusing error.
 */
template <class T>
void makeHandle (const ReadDecorHandleKey<T>& /*key*/)
{
  // If you see an error from here, you've forgotten the explicit template
  // argument to @c makeHandle giving the decoration type.
  // See the examples of @c makeHandle above.
  return T::makeHandleForDecorationsRequiresExplicitTemplateArgument();
}
template <class T>
void makeHandle (const ReadDecorHandleKey<T>& /*key*/,
                 const EventContext& /*ctx*/)
{
  // If you see an error from here, you've forgotten the explicit template
  // argument to @c makeHandle giving the decoration type.
  // See the examples of @c makeHandle above.
  return T::makeHandleForDecorationsRequiresExplicitTemplateArgument();
}
 
 
} // namespace SG