CollectionGetterTool.icc

Go to the documentation of this file.

/*
  Copyright (C) 2002-2024 CERN for the benefit of the ATLAS collaboration
*/
/**
 * @file D3PDMakerUtils/CollectionGetterTool.h 
 * @author scott snyder <snyder@bnl.gov>
 * @date Aug, 2009
 * @brief Type-safe wrapper for collection getter tools.
 */
 
 
#include <type_traits>
 
 
namespace D3PD {
 
 
/****************************************************************************
 * Helpers to deal with dereferencing container iterators.
 *
 * We want to return a pointer to an element.  For an ordinary CONT<T>,
 * it's easy, we just need &*it.
 *
 * However, a DataVector<T> actually contains T*'s, so in this case,
 * we need to return the container element directly, not a pointer to it.
 * (Note that null pointers in a DV will automatically be skipped in the
 * iteration.)  Similarly, if we have containers of @c ElementLink
 * or @c DataLink, then we don't want to return a pointer to the link;
 * we want to dereference the link and return a pointer to the target.
 * ??? Is this really the proper behavior for a link?
 */
 
 
template <class CONT, class T = typename CONT::value_type>
struct Deref
{
  typedef typename CONT::const_iterator iterator;
  typedef T type;
  static const type* deref (const iterator& it) { return &*it; }
};
 
template <class CONT, class T>
struct Deref<CONT, T*>
{
  typedef typename CONT::const_iterator iterator;
  typedef T type;
  static const type* deref (const iterator& p) { return *p; }
};
 
template <class CONT, class T>
struct Deref<CONT, ElementLink<T> >
{
  typedef typename CONT::const_iterator iterator;
  typedef typename ElementLink<T>::ElementType ElementType;
  typedef typename std::remove_pointer<ElementType>::type type;
  static const type* deref (const iterator& p) { return *(p->cptr()); }
};
 
template <class CONT, class T>
struct Deref<CONT, DataLink<T> >
{
  typedef typename CONT::const_iterator iterator;
  typedef T type;
  static const type* deref (const iterator& p) { return **p; }
};
 
 
/****************************************************************************/
 
 
/**
 * @brief Return the target object.
 * @param allowMissing If true, then we should not generate errors
 *        if the requested object is missing.
 *
 * Should be of the type given by @c typeinfo.
 * Return 0 on failure.
 *
 * This is implemented by calling @c get().
 */
template <class CONT>
const void*
CollectionGetterTool<CONT>::getUntyped (bool allowMissing /*= false*/)
{
  return get (allowMissing);
}
 
 
/**
 * @brief Return the type of the collection object retrieved by this tool.
 */
template <class CONT>
const std::type_info& CollectionGetterTool<CONT>::typeinfo() const
{
  return typeid(CONT);
}
 
 
/**
 * @brief Return the element type of the collection.
 *
 * I.e., @c nextUntyped returns a pointer to this type.
 */
template <class CONT>
const std::type_info&
CollectionGetterTool<CONT>::elementTypeinfo() const
{
  return typeid(typename Deref<CONT>::type);
}
 
 
/**
 * @brief Reset the iteration to the start of the collection.
 * @param allowMissing If true, then we should not generate errors
 *        if the requested object is missing.
 *
 * Return failure if the container cannot be retrieved.
 */
template <class CONT>
StatusCode CollectionGetterTool<CONT>::reset (bool allowMissing /*= false*/)
{
  const CONT* cont = get (allowMissing);
  if (!cont) {
    m_it = m_end;
    return allowMissing ? StatusCode::SUCCESS : StatusCode::FAILURE;
  }
 
  m_it = cont->begin();
  m_end = cont->end();
  return StatusCode::SUCCESS;
}
 
 
/**
 * @brief Return a pointer to the next element in the collection.
 *
 * Return 0 when the collection has been exhausted.
 */
template <class CONT>
const void* CollectionGetterTool<CONT>::nextUntyped()
{
  // Don't return 0 until we get to the end of the iteration.
  while (m_it != m_end) {
    const void* ret = Deref<CONT>::deref (m_it);
    ++m_it;
    if (ret) return ret;
  }
  return 0;
}
 
 
/**
 * @brief Return an estimate of the number of elements in the iteration.
 * @param allowMissing If true, then we should not generate errors
 *        if the requested object is missing.
 *
 * This can be used to pre-allocate memory.
 * (It's possible that this isn't known in advance of
 * iterating over the entire collection, for example
 * if a selection is being applied, so this is only a hint.)
 */
template <class CONT>
size_t CollectionGetterTool<CONT>::sizeHint (bool allowMissing /*= false*/)
{
  const CONT* cont = get (allowMissing);
  if (cont)
    return cont->size();
  return 0;
}
 
 
/**
 * @brief Release an object retrieved from the getter.
 * @param p The object to release.
 *
 * Call this when you are done with the object returned by
 * @c get().  The default implementation is a no-op,
 * but if the getter dynamically allocated the object which
 * it returned, this gives it a chance to free it.
 */
template <class CONT>
void CollectionGetterTool<CONT>::releaseObject (const CONT* /*p*/)
{
}
 
 
/**
 * @brief Release an object retrieved from the getter.
 * @param p The object to release.
 *
 * Call this when you are done with the object returned by
 * @c getUntyped().  The default implementation is a no-op,
 * but if the getter dynamically allocated the object which
 * it returned, this gives it a chance to free it.
 */
template <class CONT>
void CollectionGetterTool<CONT>::releaseObjectUntyped (const void* p)
{
  releaseObject (reinterpret_cast<const CONT*> (p));
}
 
 
} // namespace D3PD