bslalg_autoarraydestructor.h

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/// @file bslalg_autoarraydestructor.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslalg_autoarraydestructor.h                                       -*-C++-*-
#ifndef INCLUDED_BSLALG_AUTOARRAYDESTRUCTOR
#define INCLUDED_BSLALG_AUTOARRAYDESTRUCTOR
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslalg_autoarraydestructor bslalg_autoarraydestructor
/// @brief  Provide a proctor for destroying arrays.
/// @addtogroup bsl
/// @{
/// @addtogroup bslalg
/// @{
/// @addtogroup bslalg_autoarraydestructor
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslalg_autoarraydestructor-purpose"> Purpose</a>
/// * <a href="#bslalg_autoarraydestructor-classes"> Classes </a>
/// * <a href="#bslalg_autoarraydestructor-description"> Description </a>
///   * <a href="#bslalg_autoarraydestructor-usage"> Usage </a>
///     * <a href="#bslalg_autoarraydestructor-example-1-managing-an-array-under-construction"> Example 1: Managing an Array Under Construction </a>
///
/// # Purpose {#bslalg_autoarraydestructor-purpose}
/// Provide a proctor for destroying arrays.
///
/// # Classes {#bslalg_autoarraydestructor-classes}
///
/// -  bslalg::AutoArrayDestructor: exception-neutrality proctor for arrays
///
/// @see  bslma_autodestructor
///
/// # Description {#bslalg_autoarraydestructor-description}
/// This component provides a proctor object to manage a contiguous
/// (in-place) sequence of otherwise-unmanaged instances of a user-defined type.
/// If not explicitly released, all objects managed by the proctor object are
/// automatically destroyed by the proctor's destructor, using the
/// @ref bslalg_arraydestructionprimitives .
///
/// In most instances, `bslma::AutoDestructor` can also be used, but this
/// component is more useful in cases where it is simpler to think in terms of
/// two pointers at the ends of the array being managed, rather than an origin
/// and offset.
///
/// ## Usage {#bslalg_autoarraydestructor-usage}
///
///
/// In this section we show intended use of this component.
///
/// ### Example 1: Managing an Array Under Construction {#bslalg_autoarraydestructor-example-1-managing-an-array-under-construction}
///
///
/// In most instances, the use of a `bslalg::AutoArrayDestructor` could be
/// handled by a `bslma::AutoDeallocator`, but sometimes it is conceptually
/// clearer to frame the problem in terms of a pair of pointers rather than a
/// pointer and an offset.
///
/// Suppose we have a class, `UsageType` that allocates a block of memory upon
/// construction, and whose constructor takes a `char`.  Suppose we want to
/// create an array of elements of such objects in an exception-safe manner.
///
/// First, we create the type `UsageType`:
/// @code
///                              // ===============
///                              // class UsageType
///                              // ===============
///
/// /// This test type contains a 'char' in some allocated storage.  It has
/// /// no traits other than using a 'bslma' allocator.
/// class UsageType {
///
///     char             *d_data_p;         // managed single char
///     bslma::Allocator *d_allocator_p;    // allocator (held, not owned)
///
///   public:
///     // CREATORS
///     explicit UsageType(char c, bslma::Allocator *basicAllocator = 0)
///     : d_data_p(0)
///     , d_allocator_p(bslma::Default::allocator(basicAllocator))
///     {
///         d_data_p  = (char *)d_allocator_p->allocate(sizeof(char));
///         *d_data_p = c;
///     }
///
///     ~UsageType()
///     {
///         *d_data_p = '_';
///         d_allocator_p->deallocate(d_data_p);
///         d_data_p = 0;
///     }
///
///     // ACCESSORS
///     char datum() const
///     {
///         return *d_data_p;
///     }
/// };
///
/// namespace BloombergLP {
/// namespace bslma {
///
/// template <>
/// struct UsesBslmaAllocator<UsageType> : bsl::true_type {};
///
/// }  // close package namespace
/// }  // close enterprise namespace
/// @endcode
/// Then, in `main`, we create a `TestAllocator` to supply memory (and to verify
/// that no memory is leaked):
/// @code
/// bslma::TestAllocator ta;
/// @endcode
/// Next, we create the pointer for our array:
/// @code
/// UsageType *array;
/// @endcode
/// Then, we declare a string of characters we will use to initialize the
/// `UsageType` objects in our array.
/// @code
/// const char   *DATA = "Hello";
/// const size_t  DATA_LEN = std::strlen(DATA);
/// @endcode
/// Next, we verify that even right after exceptions have been thrown and
/// caught, no memory is outstanding:
/// @code
/// assert(0 == ta.numBlocksInUse());
/// @endcode
/// Then, we allocate our array and create a guard to free it if a subsequent
/// allocation throws an exception:
/// @code
/// array = (UsageType *) ta.allocate(DATA_LEN * sizeof(UsageType));
/// bslma::DeallocatorProctor<bslma::Allocator> arrayProctor(array, &ta);
/// @endcode
/// Next, we establish an `AutoArrayDestructor` on `array` to destroy any valid
/// elements in `array` if an exception is thrown:
/// @code
/// bslalg::AutoArrayDestructor<UsageType,> arrayElementProctor(array, array);
/// @endcode
/// Notice that we pass `arrayElementProctor` pointers to the beginning and end
/// of the range to be guarded (we start with an empty range since no elements
/// have been constructed yet).
///
/// Then, we iterate through the valid chars in `DATA` and use them to construct
/// the elements of the array:
/// @code
/// UsageType *resultElement = array;
/// for (const char *nextChar = DATA; *nextChar; ++nextChar) {
/// @endcode
/// Next, construct the next element of `array`:
/// @code
///     new (resultElement++) UsageType(*nextChar, &ta);
/// @endcode
/// Now, move the end of `arrayElementProctor` to cover the most recently
/// constructed element:
/// @code
///     arrayElementProctor.moveEnd(1);
/// }
/// @endcode
/// At this point, we have successfully created our array.
///
/// Then, release the guards so they won't destroy our work when they go out of
/// scope:
/// @code
/// arrayProctor.release();
/// arrayElementProctor.release();
/// @endcode
/// Next, exit the exception testing block:
///
/// Then, verify that the array we have created is as expected:
/// @code
/// assert('H' == array[0].datum());
/// assert('e' == array[1].datum());
/// assert('l' == array[2].datum());
/// assert('l' == array[3].datum());
/// assert('o' == array[4].datum());
/// @endcode
/// Finally, destroy & free our work and verify that no memory is leaked:
/// @code
/// for (size_t i = 0; i < DATA_LEN; ++i) {
///     array[i].~UsageType();
/// }
/// ta.deallocate(array);
///
/// assert(0 == ta.numBlocksInUse());
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslalg
 * @{
 */
/** @addtogroup bslalg_autoarraydestructor
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslalg_arraydestructionprimitives.h>
 
#include <bslma_bslallocator.h>
 
#include <bsls_assert.h>
 
#include <cstddef>  // size_t
 
 
 
namespace bslalg {
 
                        // =========================
                        // class AutoArrayDestructor
                        // =========================
 
/// This `class` provides a specialized proctor object that, upon
/// destruction and unless the `release` method has been called, destroys
/// the elements in a segment of an array of parameterized type
/// `OBJECT_TYPE`.  The elements destroyed are delimited by the "guarded"
/// range `[ begin(), end() )`.
///
/// See @ref bslalg_autoarraydestructor 
template <class OBJECT_TYPE, class ALLOCATOR = bsl::allocator<OBJECT_TYPE> >
class AutoArrayDestructor {
 
    // DATA
    OBJECT_TYPE *d_begin_p;    // address of first element in guarded range
    OBJECT_TYPE *d_end_p;      // first address beyond last element in guarded
                               // range
    ALLOCATOR    d_allocator;  // allocator
 
  private:
    // NOT IMPLEMENTED
    AutoArrayDestructor(const AutoArrayDestructor&);
    AutoArrayDestructor& operator=(const AutoArrayDestructor&);
 
  public:
    // TYPES
    typedef std::ptrdiff_t difference_type;
 
    // CREATORS
 
    /// Create an array exception guard object for the sequence of elements
    /// of the parameterized `OBJECT_TYPE` delimited by the range specified
    /// by `[ begin, end )`.  The behavior is undefined unless
    /// `begin <= end` and each element in the range `[ begin, end )` has
    /// been initialized.
    AutoArrayDestructor(OBJECT_TYPE *begin, OBJECT_TYPE *end,
                        ALLOCATOR allocator = ALLOCATOR());
 
    /// Call the destructor on each of the elements of the parameterized
    /// `OBJECT_TYPE` delimited by the range `[ begin(), end() )` and
    /// destroy this array exception guard.
    ~AutoArrayDestructor();
 
    // MANIPULATORS
 
    /// Move the begin pointer by the specified `offset`, and return the new
    /// begin pointer.
    OBJECT_TYPE *moveBegin(difference_type offset = -1);
 
    /// Move the end pointer by the specified `offset`, and return the new
    /// end pointer.
    OBJECT_TYPE *moveEnd(difference_type offset = 1);
 
    /// Set the range of elements guarded by this object to be empty.  Note
    /// that `begin() == end()` following this operation, but the specific
    /// value is unspecified.
    void release();
};
 
// ============================================================================
//                          INLINE FUNCTION DEFINITIONS
// ============================================================================
 
                      // -------------------------
                      // class AutoArrayDestructor
                      // -------------------------
 
// CREATORS
template <class OBJECT_TYPE, class ALLOCATOR>
inline
AutoArrayDestructor<OBJECT_TYPE, ALLOCATOR>::AutoArrayDestructor(
                                                        OBJECT_TYPE *begin,
                                                        OBJECT_TYPE *end,
                                                        ALLOCATOR    allocator)
: d_begin_p(begin)
, d_end_p(end)
, d_allocator(allocator)
{
    BSLS_ASSERT_SAFE(!begin == !end);
    BSLS_ASSERT_SAFE(begin <= end);
}
 
template <class OBJECT_TYPE, class ALLOCATOR>
inline
AutoArrayDestructor<OBJECT_TYPE, ALLOCATOR>::~AutoArrayDestructor()
{
    BSLS_ASSERT_SAFE(!d_begin_p == !d_end_p);
    BSLS_ASSERT_SAFE(d_begin_p <= d_end_p);
 
    ArrayDestructionPrimitives::destroy(d_begin_p, d_end_p, d_allocator);
}
 
// MANIPULATORS
template <class OBJECT_TYPE, class ALLOCATOR>
inline
OBJECT_TYPE *AutoArrayDestructor<OBJECT_TYPE, ALLOCATOR>::moveBegin(
                                                        difference_type offset)
{
    BSLS_ASSERT_SAFE(d_begin_p || 0 == offset);
    BSLS_ASSERT_SAFE(d_end_p - d_begin_p >= offset);
 
    d_begin_p += offset;
    return d_begin_p;
}
 
template <class OBJECT_TYPE, class ALLOCATOR>
inline
OBJECT_TYPE *
AutoArrayDestructor<OBJECT_TYPE, ALLOCATOR>::moveEnd(difference_type offset)
{
    BSLS_ASSERT_SAFE(d_end_p || 0 == offset);
    BSLS_ASSERT_SAFE(d_end_p - d_begin_p >= -offset);
 
    d_end_p += offset;
    return d_end_p;
}
 
template <class OBJECT_TYPE, class ALLOCATOR>
inline
void AutoArrayDestructor<OBJECT_TYPE, ALLOCATOR>::release()
{
    d_begin_p = d_end_p;
}
 
}  // close package namespace
 
#ifndef BDE_OPENSOURCE_PUBLICATION  // BACKWARD_COMPATIBILITY
// ============================================================================
//                           BACKWARD COMPATIBILITY
// ============================================================================
 
#ifdef bslalg_AutoArrayDestructor
#undef bslalg_AutoArrayDestructor
#endif
/// This alias is defined for backward compatibility.
#define bslalg_AutoArrayDestructor bslalg::AutoArrayDestructor
#endif  // BDE_OPENSOURCE_PUBLICATION -- BACKWARD_COMPATIBILITY
 
 
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2013 Bloomberg Finance L.P.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// ----------------------------- END-OF-FILE ----------------------------------
 
/** @} */
/** @} */
/** @} */