bslalg_functoradapter.h

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/// @file bslalg_functoradapter.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslalg_functoradapter.h                                            -*-C++-*-
#ifndef INCLUDED_BSLALG_FUNCTORADAPTER
#define INCLUDED_BSLALG_FUNCTORADAPTER
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslalg_functoradapter bslalg_functoradapter
/// @brief  Provide an utility that adapts callable objects to functors.
/// @addtogroup bsl
/// @{
/// @addtogroup bslalg
/// @{
/// @addtogroup bslalg_functoradapter
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslalg_functoradapter-purpose"> Purpose</a>
/// * <a href="#bslalg_functoradapter-classes"> Classes </a>
/// * <a href="#bslalg_functoradapter-description"> Description </a>
///   * <a href="#bslalg_functoradapter-usage"> Usage </a>
///     * <a href="#bslalg_functoradapter-example-1-using-function-pointer-base-for-an-empty-base-optimized-class"> Example 1: Using function pointer base for an empty-base optimized class </a>
///
/// # Purpose {#bslalg_functoradapter-purpose}
/// Provide an utility that adapts callable objects to functors.
///
/// # Classes {#bslalg_functoradapter-classes}
///
/// -   bslalg::FunctorAdapter: utility for using callable objects as functors
///
/// @see  bslstl_setcomparator, bslstl_mapcomparator
///
/// # Description {#bslalg_functoradapter-description}
/// This component provides a single utility template,
/// `FunctorAdapter`, that adapts a parameterized adaptee type, which can be any
/// callable object type, to a target functor type.  This adaptation enables a
/// client to inherit from the target functor type even if the adaptee callable
/// object type is a function pointer type.  This is particularly useful if the
/// client of the callable object type wants to take advantage of the empty-base
/// optimization to avoid paying storage cost when the callable object type is a
/// functor type with no data members.
///
/// `FunctorAdapter` defines an alias to the target functor type.  If the
/// adaptee type is a functor type, the target type is an alias to the adaptee
/// type.  If the adaptee type is a function pointer type, the target type is a
/// functor type that delegates to a function referred to by a function pointer
/// of the adaptee type.
///
/// ## Usage {#bslalg_functoradapter-usage}
///
///
/// This section illustrates the intended use of this component.
///
/// ### Example 1: Using function pointer base for an empty-base optimized class {#bslalg_functoradapter-example-1-using-function-pointer-base-for-an-empty-base-optimized-class}
///
///
/// Suppose that we wanted to define a binder that binds a binary predicate of a
/// parameterized type to a value passed on construction.  Also suppose that we
/// wanted to use the empty-base optimization to avoid paying storage cost when
/// the predicate type is a functor type with no data members.  Unfortunately,
/// the binary predicate type may be a function pointer type, which cannot serve
/// as a base class.  The solution is to have the binder inherit from
/// `FunctorAdapter::Type`, which adapts a function pointer type to a functor
/// type that is a suitable base class.
///
/// First, we define the class `Bind2ndInteger`, which inherits from
/// `FunctorAdapter::Type` to take advantage of the empty-base optimization:
/// @code
/// /// This class provides a functor that delegate its function-call
/// /// operator to the parameterized `BINARY_PREDICATE`, passing the user
/// /// supplied parameter as the first argument and the integer value
/// /// passed on construction as the second argument.
/// template <class BINARY_PREDICATE>
/// class Bind2ndInteger : private FunctorAdapter<BINARY_PREDICATE>::Type {
///
///     // DATA
///     int d_bondValue;  // the bound value
///
///     // NOT IMPLEMENTED
///     Bind2ndInteger(const Bind2ndInteger&);
///     Bind2ndInteger& operator=(const Bind2ndInteger&);
///
///   public:
///     // CREATORS
///
///     /// Create a `Bind2ndInteger` object that will bind the second
///     /// parameter of the specified `predicate` with the specified
///     /// integer `value`.
///     Bind2ndInteger(int value, const BINARY_PREDICATE& predicate);
///
///     /// Destroy this object.
///     //! ~Bind2ndInteger() = default;
///
///     // ACCESSORS
///
///     /// Return the result of calling the parameterized
///     /// `BINARY_PREDICATE` passing the specified `value` as the first
///     /// argument and the integer value passed on construction as the
///     /// second argument.
///     bool operator() (const int value) const;
/// };
/// @endcode
///  Then, we implement the methods of the `Bind2ndInteger` class:
/// @code
/// template <class BINARY_PREDICATE>
/// Bind2ndInteger<BINARY_PREDICATE>::Bind2ndInteger(int value,
///                                         const BINARY_PREDICATE& predicate)
/// : FunctorAdapter<BINARY_PREDICATE>::Type(predicate), d_bondValue(value)
/// {
/// }
/// @endcode
/// Here, we implement the `operator()` member function that simply delegates to
/// `BINARY_PREDICATE`
/// @code
/// template <class BINARY_PREDICATE>
/// bool Bind2ndInteger<BINARY_PREDICATE>::operator() (const int value) const
/// {
///     const BINARY_PREDICATE& predicate = *this;
///     return predicate(value, d_bondValue);
/// }
/// @endcode
/// Next, we define a function, `intCompareFunction`, that compares two
/// integers:
/// @code
/// bool intCompareFunction(const int lhs, const int rhs)
/// {
///     return lhs < rhs;
/// }
/// @endcode
/// Now, we define a `Bind2ndInteger` object `functorLessThan10` using the
/// `std::less<int>` functor as the parameterized `BINARY_PREDICATE` and invoke
/// the function call operator:
/// @code
/// Bind2ndInteger<std::less<int> > functorLessThan10(10, std::less<int>());
///
/// assert(functorLessThan10(1));
/// assert(!functorLessThan10(12));
/// @endcode
/// Finally, we define a `Bind2ndInteger` object `functionLessThan10` passing
/// the address of `intCompareFunction` on construction and invoke the function
/// call operator:
/// @code
/// Bind2ndInteger<bool (*)(const int, const int)>
///                                functionLessThan10(10, &intCompareFunction);
///
/// assert(functionLessThan10(1));
/// assert(!functionLessThan10(12));
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslalg
 * @{
 */
/** @addtogroup bslalg_functoradapter
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslmf_assert.h>
#include <bslmf_functionpointertraits.h>
 
#include <bsls_assert.h>
 
 
namespace bslalg {
 
                    // ====================================
                    // class FunctorAdapter_FunctionPointer
                    // ====================================
 
/// This class provides a functor that delegates to the function referred to
/// by a function pointer supplied on construction.  Delegation is supported
/// through the conversion operator, which implicitly returns a reference to
/// the parameterized `FUNCTION_POINTER`.
///
/// See @ref bslalg_functoradapter 
template <class FUNCTION_POINTER>
class FunctorAdapter_FunctionPointer {
 
  private:
    // DATA
    FUNCTION_POINTER d_function_p;  // the pointer to the function
 
  public:
    // CREATORS
 
    /// Create a `FunctorAdapter_FunctionPointer` object that will delegate
    /// to the function referred to by the specified `functionPtr`.
    explicit FunctorAdapter_FunctionPointer(FUNCTION_POINTER functionPtr);
 
    // MANIPULATORS
 
    /// Convert this object to the parameterized `FUNCTION_POINTER` by
    /// returning the function pointer supplied on construction.
    operator FUNCTION_POINTER& ();
 
    // ACCESSORS
 
    /// Convert this object to the parameterized `FUNCTION_POINTER` by
    /// returning the function pointer supplied on construction.
    operator const FUNCTION_POINTER& () const;
};
 
                    // ====================
                    // class FunctorAdapter
                    // ====================
 
/// This class provides a metafunction that defines an alias `Type` for the
/// parameterized `CALLABLE_OBJECT`.  `Type` is functor type that provides
/// the same operation as the parameterized `CALLABLE_OBJECT`.  Note that
/// function pointers are supported through a specialization of this
/// template.
///
/// See @ref bslalg_functoradapter 
template <class CALLABLE_OBJECT>
class FunctorAdapter {
 
  public:
    // PUBLIC TYPES
 
    /// This `typedef` is an alias for the functor.
    typedef CALLABLE_OBJECT Type;
};
 
                    // ====================
                    // class FunctorAdapter
                    // ====================
 
/// This specialization of `FunctorAdapter` defines an alias `Type` for a
/// functor that delegates to a function pointer matching the parameterized
/// `FUNCTION` type.
template <class FUNCTION>
class FunctorAdapter<FUNCTION*> {
 
    BSLMF_ASSERT(bslmf::IsFunctionPointer<FUNCTION*>::value);
        // This 'BSLMF_ASSERT' statement ensures that the parameter 'FUNCTION'
        // must be a function pointer.
 
  public:
    // PUBLIC TYPES
 
    /// This `typedef` is an alias for a functor that delegates to the function
    /// referred to by the function pointer matching the parameterized
    /// `FUNCTION` type.
    typedef FunctorAdapter_FunctionPointer<FUNCTION*> Type;
};
 
 
// ============================================================================
//                  TEMPLATE AND INLINE FUNCTION DEFINITIONS
// ============================================================================
 
                    // ------------------------------------
                    // class FunctorAdapter_FunctionPointer
                    // ------------------------------------
 
// CREATORS
template <class FUNCTION_POINTER>
inline
FunctorAdapter_FunctionPointer<FUNCTION_POINTER>
::FunctorAdapter_FunctionPointer(FUNCTION_POINTER functionPtr)
:d_function_p(functionPtr)
{
}
 
// MANIPULATORS
template <class FUNCTION_POINTER>
inline
FunctorAdapter_FunctionPointer<FUNCTION_POINTER>
::operator FUNCTION_POINTER& ()
{
    return d_function_p;
}
 
// ACCESSORS
template <class FUNCTION_POINTER>
inline
FunctorAdapter_FunctionPointer<FUNCTION_POINTER>
::operator const FUNCTION_POINTER& () const
{
    return d_function_p;
}
 
}  // close package namespace
 
 
 
#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 ----------------------------------
 
/** @} */
/** @} */
/** @} */