bslstl_stringrefdata.h

Go to the documentation of this file.

/// @file bslstl_stringrefdata.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslstl_stringrefdata.h                                             -*-C++-*-
#ifndef INCLUDED_BSLSTL_STRINGREFDATA
#define INCLUDED_BSLSTL_STRINGREFDATA
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslstl_stringrefdata bslstl_stringrefdata
/// @brief  Provide a base class for `bslstl::StringRef`.
/// @addtogroup bsl
/// @{
/// @addtogroup bslstl
/// @{
/// @addtogroup bslstl_stringrefdata
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslstl_stringrefdata-purpose"> Purpose</a>
/// * <a href="#bslstl_stringrefdata-classes"> Classes </a>
/// * <a href="#bslstl_stringrefdata-description"> Description </a>
///   * <a href="#bslstl_stringrefdata-usage"> Usage </a>
///     * <a href="#bslstl_stringrefdata-example-1-breaking-cyclic-dependency-between-string-and-stringref"> Example 1: Breaking Cyclic Dependency Between String and StringRef </a>
///
/// # Purpose {#bslstl_stringrefdata-purpose}
/// Provide a base class for `bslstl::StringRef`.
///
/// # Classes {#bslstl_stringrefdata-classes}
///
/// -  bslstl::StringRefData: intermediate class providing StringRef compatibility
///
/// **Canonical header:**  bsl_string.h
///
/// # Description {#bslstl_stringrefdata-description}
/// Initially, this component provided a complex-constrained,
/// in-core (value-semantic) attribute class, `bslstl::StringRefData`, that
/// represented a reference to character string data.  Note that
/// `bslstl::StringRefData` was intended for use as a base class for
/// `bslstl::StringRef` and as parameter of `bsl::string` constructor, enabling
/// a conversion from `bslstl::StringRef` to `bsl::string` without having a
/// cyclic dependency among these three classes.
///
/// But nowadays it only provides compatibility between the two constructors of
/// `bsl::string` (implicit constructor, accepting `StringRefData` object by
/// value and explicit constructor, accepting `bsl::string_view` object by
/// value) to allow existing users of `bslstl::StringRef` not to change their
/// code.
///
/// The dependencies between these components are shown on the following
/// diagram:
/// @code
///                             +-----------------------+
///                             |                       |
///                    /--------o   bslstl::StringRef   |
///                   /         |                       |
///                  /          +-----------------------+
///                 /                      |
///                /                       |
/// +------------------+        +----------V------------+
/// |                  |        |                       |
/// |   bsl::string    o--------| bslstl::StringRefData |
/// |                  |        |                       |
/// +--------------o---+        +-----------------------+
///                 \                      |
///                  \                     |
///                   \         +----------V------------+
///                    \        |                       |
///                     \-------|    bsl::string_view   |
///                             |                       |
///                             +-----------------------+
/// @endcode
///
/// ## Usage {#bslstl_stringrefdata-usage}
///
///
/// This section illustrates intended use of this component.
///
/// ### Example 1: Breaking Cyclic Dependency Between String and StringRef {#bslstl_stringrefdata-example-1-breaking-cyclic-dependency-between-string-and-stringref}
///
///
/// In this example we demonstrate how `bslstl::StringRefData` allows us to
/// break the cyclic dependency between hypothetical `String` and `StringRef`
/// classes.
///
/// Objects of our `String` and `StringRef` classes need to be convertible to
/// each other.  However, only one of these classes can depend on the definition
/// of the other one, otherwise they will be cyclically dependent.
///
/// First, we define a hypothetical `String` class, whose implementation is
/// intentionally simple and contains only the essential constructors and
/// accessor methods; the important thing to notice is that `String` does not
/// depend on `StringRef`, which has not been defined yet:
/// @code
/// namespace Usage {
///
/// class String {
///   private:
///     const char *d_begin_p;
///     const char *d_end_p;
///
///   public:
///     typedef const char *const_iterator;
///
///     String(bslstl::StringRefData<char> const& stringRef)
///     : d_begin_p(stringRef.data())
///     , d_end_p(stringRef.data() + stringRef.length())
///     {}
///
///     const char *data() const
///     {
///         return d_begin_p;
///     }
///
///     std::size_t length() const
///     {
///         return static_cast<std::size_t>(d_end_p - d_begin_p);
///     }
/// };
/// @endcode
/// Notice that the constructor of `String` takes a `bslstl::StringRefData`
/// argument and then uses its members `data` and `length` to initialize the
/// string object.
///
/// Then, we define a hypothetical `StringRef` class, whose instances can be
/// initialized either with a `String` object (to enable the conversion from
/// `String` to `StringRef`) or with two `const char *` pointers:
/// @code
/// class StringRef : public bslstl::StringRefData<char>
/// {
///   public:
///     StringRef(const char *begin, const char *end)
///     : bslstl::StringRefData<char>(begin, end)
///     {}
///
///     StringRef(const String& str)
///     : bslstl::StringRefData<char>(str.data(), str.data() + str.length())
///     {}
/// };
///
/// }  // close namespace Usage
/// @endcode
/// Note that `StringRef` also derives from `bslstl::StringRefData` so that an
/// object of `StringRef` can be passed to the constructor of `String` as a
/// reference to `bslstl::StringRefData`, which enables the conversion from
/// `StringRef` to `String`.
///
/// Finally, we verify that the conversions between `String` and `StringRef`
/// work:
/// @code
/// using Usage::String;
/// using Usage::StringRef;
///
/// const char str[] = "test string";
/// StringRef  strRef(str, str + sizeof(str));
///
/// String     strObj = strRef;     // convert `StringRef` to `String`
/// StringRef  strRf2 = strObj;     // convert `String` to `StringRef`
///
/// assert(strObj.data()   == strRef.data());
/// assert(strObj.length() == strRef.length());
/// assert(strObj.data()   == strRf2.data());
/// assert(strObj.length() == strRf2.length());
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslstl
 * @{
 */
/** @addtogroup bslstl_stringrefdata
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslstl_stringview.h>
 
#include <bslmf_istriviallycopyable.h>
#include <bslmf_nestedtraitdeclaration.h>
 
#include <bsls_assert.h>
 
#include <iosfwd>
 
#ifndef BDE_DONT_ALLOW_TRANSITIVE_INCLUDES
#include <bsls_nativestd.h>
#endif // BDE_DONT_ALLOW_TRANSITIVE_INCLUDES
 
 
 
namespace bslstl {
 
                         // ===================
                         // class StringRefData
                         // ===================
 
/// This class is an intermediate link between `bslstl::StringRef` used in
/// BDE and `bsl::string_view` and is kept only for compatibility with
/// legacy code.
///
/// See @ref bslstl_stringrefdata 
template <class CHAR_TYPE>
class StringRefData : public bsl::basic_string_view<CHAR_TYPE> {
 
  private:
    // PRIVATE TYPES
    typedef bsl::basic_string_view<CHAR_TYPE> Base;
 
  public:
    // CLASS METHODS
 
    /// Return the number of `CHAR_TYPE` characters in the specified
    /// null-terminated `data` string, up to but not including the terminal
    /// null value.
    static std::size_t cStringLength(const CHAR_TYPE *data);
 
    // TRAITS
    BSLMF_NESTED_TRAIT_DECLARATION(StringRefData, bsl::is_trivially_copyable);
 
    // CREATORS
 
    /// Create a `StringRefData` object having default attribute values:
    /// @code
    /// begin() == 0
    /// end()   == 0
    /// @endcode
    StringRefData();
 
    /// Create a `StringRefData` object the specified `begin` and `end`
    /// attribute values.  The behavior is undefined unless `begin <= end`
    /// and `!begin == !end`.
    StringRefData(const CHAR_TYPE *begin, const CHAR_TYPE *end);
 
    /// Create a `StringRefData` object from the specified `view`.
    explicit StringRefData(const bsl::basic_string_view<CHAR_TYPE>& view);
 
     StringRefData(const StringRefData&) = default;
     ~StringRefData() = default;
 
    // MANIPULATORS
     StringRefData& operator=(const StringRefData&) = default;
 
};
 
// ============================================================================
//                       TEMPLATE FUNCTION DEFINITIONS
// ============================================================================
 
                         // -------------------
                         // class StringRefData
                         // -------------------
 
// CLASS METHODS
template <class CHAR_TYPE>
inline
std::size_t StringRefData<CHAR_TYPE>::cStringLength(
                                                         const CHAR_TYPE *data)
{
    BSLS_ASSERT_SAFE(data);
 
    return std::char_traits<CHAR_TYPE>::length(data);
}
 
// CREATORS
template <class CHAR_TYPE>
inline
StringRefData<CHAR_TYPE>::StringRefData()
: Base()
{
}
 
template <class CHAR_TYPE>
inline
StringRefData<CHAR_TYPE>
    ::StringRefData(const CHAR_TYPE *begin,
                    const CHAR_TYPE *end)
: Base(begin, end - begin)
{
    BSLS_ASSERT_SAFE(begin <= end);
    BSLS_ASSERT_SAFE(!begin == !end);
}
 
template <class CHAR_TYPE>
inline
StringRefData<CHAR_TYPE>
    ::StringRefData(const bsl::basic_string_view<CHAR_TYPE>& view)
: Base(view)
{
}
 
}  // close package namespace
 
#ifndef BDE_OPENSOURCE_PUBLICATION  // BACKWARD_COMPATIBILITY
// ============================================================================
//                           BACKWARD COMPATIBILITY
// ============================================================================
 
#ifdef bslstl_StringRefData
#undef bslstl_StringRefData
#endif
/// This alias is defined for backward compatibility.
#define bslstl_StringRefData bslstl::StringRefData
#endif  // BDE_OPENSOURCE_PUBLICATION -- BACKWARD_COMPATIBILITY
 
 
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2019 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 ----------------------------------
 
/** @} */
/** @} */
/** @} */