bslmf_integersequence.h

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/// @file bslmf_integersequence.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslmf_integersequence.h                                            -*-C++-*-
#ifndef INCLUDED_BSLMF_INTEGERSEQUENCE
#define INCLUDED_BSLMF_INTEGERSEQUENCE
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslmf_integersequence bslmf_integersequence
/// @brief  Provide a template parameter pack of integers.
/// @addtogroup bsl
/// @{
/// @addtogroup bslmf
/// @{
/// @addtogroup bslmf_integersequence
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslmf_integersequence-purpose"> Purpose</a>
/// * <a href="#bslmf_integersequence-classes"> Classes </a>
/// * <a href="#bslmf_integersequence-description"> Description </a>
///   * <a href="#bslmf_integersequence-usage"> Usage </a>
///     * <a href="#bslmf_integersequence-example-1-pass-c-array-as-a-parameter-to-a-function-with-variadic-template"> Example 1: Pass C-array as a parameter to a function with variadic template </a>
///
/// # Purpose {#bslmf_integersequence-purpose}
/// Provide a template parameter pack of integers.
///
/// # Classes {#bslmf_integersequence-classes}
///
/// -  bslmf::IntegerSequence: a compile-time sequence of integers
///
/// # Description {#bslmf_integersequence-description}
/// This component defines a class template,
/// `bslmf::IntegerSequence`, which can be used in parameter pack expansions.
///
/// `bslmf::IntegerSequence` meets the requirements of the @ref integer_sequence 
/// template introduced in the C++14 standard [intseq.intseq] and can be used in
/// a client's code if the compiler supports the C++11 standard.
///
/// Note, that this component has no (emulated) support for pre-standard C++11
/// compilers, as its only purpose is to be used in deduction with template
/// parameter packs.  There is no language support to emulate in earlier
/// compilers.
///
/// ## Usage {#bslmf_integersequence-usage}
///
///
/// In this section we show intended use of this component.
///
/// ### Example 1: Pass C-array as a parameter to a function with variadic template {#bslmf_integersequence-example-1-pass-c-array-as-a-parameter-to-a-function-with-variadic-template}
///
///
/// Suppose we want to initialize a C-Array of known size `t_N` with data read
/// from a data source using a library class that provides a variadic template
/// interface that loads a data of variable length into the supplied parameter
/// pack.
///
/// First, define a class template `DataReader`,
/// @code
/// template <std::size_t t_N>
/// class DataReader {
///   public:
/// @endcode
/// Then, implement a method that loads the specified parameter pack `args` with
/// data read from a data source.
/// @code
///    template <class ...t_T>
///    void read(t_T*... args) const
///    {
///        static_assert(sizeof...(args) == t_N, "");
///        read_impl(args...);
///    }
/// @endcode
/// Next, for the test purpose provide simple implementation of the recursive
/// variadic @ref read_impl  function that streams the index of the C-Array's
/// element to `stdout`.
/// @code
/// private:
///     template <class t_U, class ...t_T>
///     void read_impl(t_U*, t_T*... args) const
///     {
///         printf("read element #%i\n",
///                static_cast<int>(t_N - 1 - sizeof...(args)));
///         read_impl(args...);
///     }
/// @endcode
/// Then, implement the recursion break condition.
/// @code
///    void read_impl() const
///    {
///    }
/// };
/// @endcode
/// Next, define a helper function template `readData` that expands the
/// parameter pack of indices `t_I` and invokes the variadic template `read`
/// method of the specified `reader` object.
/// @code
/// namespace {
/// template<class t_R, class t_T, std::size_t... t_I>
/// void readData(const t_R&  reader,
///               t_T      *data,
///               bslmf::IntegerSequence<std::size_t, t_I...>)
/// {
///     reader.read(&data[t_I]...);
///         // In pseudocode, this is equivalent to:
///         // reader.read(&data[0],
///         //             &data[1],
///         //             &data[2],
///         //             ...
///         //             &data[t_N-1]);
/// }
/// }
/// @endcode
/// Finally, define a `data` C-Array and `reader` variables and pass them to the
/// `readData` function as parameters.
/// @code
/// constexpr int      k_SIZE = 5;
/// DataReader<k_SIZE> reader;
/// int                data[k_SIZE] = {0};
///
/// readData(reader,
///          data,
///          bslmf::IntegerSequence<size_t, 0, 1, 2, 3, 4>());
/// @endcode
/// Note that using a direct call to the `bslmf::IntegerSequence` constructor
/// looks a bit clumsy here.  The better approach is to use alias template
/// `bslmf::MakeIntegerSequence`, that creates a collection of increasing
/// integer values, having the specified t_N-value length.  The usage example in
/// that component shows this method more clearly.  But we can not afford its
/// presence here to avoid a cycle/levelization violation.
///
/// The streaming operator produces output in the following format on `stdout`:
/// @code
/// read element #0
/// read element #1
/// read element #2
/// read element #3
/// read element #4
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslmf
 * @{
 */
/** @addtogroup bslmf_integersequence
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslmf_integralconstant.h>
 
#include <bsls_libraryfeatures.h>
 
#include <cstddef>  // 'std::size_t'
 
#ifdef BSLS_LIBRARYFEATURES_HAS_CPP14_INTEGER_SEQUENCE
 
 
namespace bslmf {
                            // ======================
                            // struct IntegerSequence
                            // ======================
 
/// This class template represents a compile-time sequence of integers.
/// When passed as an argument to a function template, the specified
/// parameter pack `t_INTS` can be deduced and used a in pack expansion.
template <class t_T, t_T ...t_INTS>
struct IntegerSequence {
 
    // TYPES
 
    /// `value_type` is an alias to the template parameter `t_T` that
    /// represents an integer type to use for the elements of the sequence.
    typedef t_T value_type;
 
    // CLASS METHODS
 
    /// Return the number of elements in `t_INTS`.
    static constexpr std::size_t size() noexcept;
};
 
}  // close package namespace
 
// ============================================================================
//                      INLINE FUNCTION DEFINITIONS
// ============================================================================
 
                            // ----------------------
                            // struct IntegerSequence
                            // ----------------------
 
template <class t_T, t_T... t_INTS>
inline
constexpr std::size_t bslmf::IntegerSequence<t_T, t_INTS...>::size() noexcept
{
    return sizeof...(t_INTS);
}
 
 
 
#endif  // BSLS_LIBRARYFEATURES_HAS_CPP14_INTEGER_SEQUENCE
 
#endif  // INCLUDED_BSLMF_INTEGERSEQUENCE
 
// ----------------------------------------------------------------------------
// Copyright 2018 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 ----------------------------------
 
/** @} */
/** @} */
/** @} */