bsla_maybeunused.h

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/// @file bsla_maybeunused.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bsla_maybeunused.h                                                 -*-C++-*-
#ifndef INCLUDED_BSLA_MAYBEUNUSED
#define INCLUDED_BSLA_MAYBEUNUSED
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bsla_maybeunused bsla_maybeunused
/// @brief  Provide a macro to suppress "unused" warnings.
/// @addtogroup bsl
/// @{
/// @addtogroup bsla
/// @{
/// @addtogroup bsla_maybeunused
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bsla_maybeunused-purpose"> Purpose</a>
/// * <a href="#bsla_maybeunused-macros"> Macros </a>
/// * <a href="#bsla_maybeunused-description"> Description </a>
///   * <a href="#bsla_maybeunused-macro-reference"> Macro Reference </a>
///   * <a href="#bsla_maybeunused-usage"> Usage </a>
///     * <a href="#bsla_maybeunused-example-1-unused-warnings"> Example 1: "Unused" Warnings </a>
///
/// # Purpose {#bsla_maybeunused-purpose}
/// Provide a macro to suppress "unused" warnings.
///
/// # Macros {#bsla_maybeunused-macros}
///
/// -  BSLA_MAYBE_UNUSED:           suppress compiler warnings on unused entities
/// -  BSLA_MAYBE_UNUSED_IS_ACTIVE: defined if `BSLA_MAYBE_UNUSED` is active
///
/// @see  bsla_annotations
///
/// # Description {#bsla_maybeunused-description}
/// This component provides a preprocessor macro that will suppress
/// "unused" warnings on a locally defined function, type, or variable that is
/// not used.
///
/// ## Macro Reference {#bsla_maybeunused-macro-reference}
///
///
///  `BSLA_MAYBE_UNUSED`:
///     This annotation indicates that the so-annotated function, variable, or
///     type is possibly unused and the compiler should not generate a warning
///     for the unused identifier.
/// 
///  `BSLA_MAYBE_UNUSED_IS_ACTIVE`:
///      The macro `BSLA_MAYBE_UNUSED_IS_ACTIVE` is defined if
///      `BSLA_MAYBE_UNUSED` expands to something with the desired effect;
///       otherwise `BSLA_MAYBE_UNUSED_IS_ACTIVE` is not defined and
///      `BSLA_MAYBE_UNUSED` expands to nothing.
///
/// ## Usage {#bsla_maybeunused-usage}
///
///
/// This section illustrates intended use of this component.
///
/// ### Example 1: "Unused" Warnings {#bsla_maybeunused-example-1-unused-warnings}
///
///
/// First, we define a namespace, `warn`, within the unnamed namespace with a
/// type, a function, and a variable in it.  They are unused:
/// @code
/// namespace {
/// namespace warn {
///
/// double x;
///
/// struct ResultRec {
///     double d_x;
///     double d_y;
/// };
///
/// int quadratic(double *zeroA,
///               double *zeroB,
///               double *zeroC,
///               double cubeFactor,
///               double a,
///               double b,
///               double c)
///     // Solve the quadratic function for the specified 'a', 'b', and 'c',
///     // where '0 = a * x^2 + b * x + c'.  If the quadratic has no solutions,
///     // return a non-zero value, and set the specified 'zeroA' and 'zeroB'
///     // to those solutions and return 0 otherwise.  The specified
///     // 'cubeFactor' and 'zeroC' are unused for now but will be used in
///     // future expansion of the function to handle cubic polynomials.
/// {
///     typedef int UnusedTypedef;
///
///     const double discriminant = b * b - 4 * a * c;
///     if (discriminant < 0 || 0.0 == a) {
///         *zeroA = *zeroB = 0.0;
///         return -1;                                                // RETURN
///     }
///
///     const double root = ::sqrt(discriminant);
///     *zeroA = (-b + root) / (2 * a);
///     *zeroB = (-b - root) / (2 * a);
///
///     return 0;
/// }
///
/// }  // close namespace warn
/// }  // close unnamed namespace
/// @endcode
/// Then, we observe the warnings:
/// @code
/// .../bsla_maybeunused.t.cpp:145:21: warning: typedef 'UnusedTypedef' locally
/// defined but not used [-Wunused-local-typedefs]
///          typedef int UnusedTypedef;
///                      ^~~~~~~~~~~~~
/// .../bsla_maybeunused.t.cpp:133:27: warning: unused parameter 'zeroC'
/// [-Wunused-parameter]
///                    double *zeroC,
///                            ^~~~~
/// .../bsla_maybeunused.t.cpp:134:26: warning: unused parameter 'cubeFactor'
/// [-Wunused-parameter]
///                    double cubeFactor,
///                           ^~~~~~~~~~
/// .../bsla_maybeunused.t.cpp:131:9: warning: 'int {anonymous}::warn::
/// quadratic(double*, double*, double*, double, double, double, double)'
/// defined but not used [-Wunused-function]
///      int quadratic(double *zeroA,
///          ^~~~~~~~~
/// .../bsla_maybeunused.t.cpp:124:12: warning: '{anonymous}::warn::x' defined
/// but not used [-Wunused-variable]
///      double x;
///             ^
/// @endcode
/// Note that none of the compilers currently in use by the development team
/// issue a warning on the unused `warn::ResultRec`, but some in the future
/// might.  In the meantime, `BSLA_MAYBE_UNUSED` is tolerated on type
/// declarations without resulting in a syntax error.
///
/// Next, we define a namespace, `nowarn`, within the unused namespace with
/// exactly the same unused entities, using the `BSLA_MAYBE_UNUSED` annotation
/// to silence the warnings:
/// @code
/// namespace {
/// namespace nowarn {
///
/// struct BSLA_MAYBE_UNUSED ResultRec {
///     double d_x;
///     double d_y;
/// };
///
/// BSLA_MAYBE_UNUSED double x;
///
/// BSLA_MAYBE_UNUSED int quadratic(double                   *zeroA,
///                                 double                   *zeroB,
///                                 BSLA_MAYBE_UNUSED double *zeroC,
///                                 BSLA_MAYBE_UNUSED double  cubeFactor,
///                                 double                    a,
///                                 double                    b,
///                                 double                    c);
///     // Solve the quadratic function for the specified 'a', 'b', and 'c',
///     // where '0 = a * x^2 + b * x + c'.  If the quadratic has no solutions,
///     // return a non-zero value, and set the specified 'zeroA' and 'zeroB'
///     // to those solutions and return 0 otherwise.  The specified
///     // 'cubeFactor' and 'zeroC' are unused for now but will be used in
///     // future expansion of the function to handle cubic polynomials.
///
/// int quadratic(double                   *zeroA,
///               double                   *zeroB,
///               BSLA_MAYBE_UNUSED double *zeroC,
///               BSLA_MAYBE_UNUSED double  cubeFactor,
///               double                    a,
///               double                    b,
///               double                    c)
/// {
///     BSLA_MAYBE_UNUSED typedef int UnusedTypedef;
///
///     const double discriminant = b * b - 4 * a * c;
///     if (discriminant < 0 || 0.0 == a) {
///         *zeroA = *zeroB = 0.0;
///         return -1;                                                // RETURN
///     }
///
///     const double root = ::sqrt(discriminant);
///     *zeroA = (-b + root) / (2 * a);
///     *zeroB = (-b - root) / (2 * a);
///
///     return 0;
/// }
///
/// }  // close namespace nowarn
/// }  // close unnamed namespace
/// @endcode
/// Finally, we observe that the warnings for the `nowarn` namespace are
/// suppressed.
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bsla
 * @{
 */
/** @addtogroup bsla_maybeunused
 * @{
 */
 
#include <bsls_compilerfeatures.h>
 
                       // =============================
                       // Checks for Pre-Defined macros
                       // =============================
 
#if defined(BSLA_MAYBE_USED)
#error BSLA_MAYBE_USED is already defined!
#endif
 
#if defined(BSLA_MAYBE_USED_IS_ACTIVE)
#error BSLA_MAYBE_USED_IS_ACTIVE is already defined!
#endif
 
                       // =========================
                       // Set macros as appropriate
                       // =========================
 
#if defined(BSLS_COMPILERFEATURES_SUPPORT_ATTRIBUTE_MAYBE_UNUSED)
    #define BSLA_MAYBE_UNUSED [[ maybe_unused ]]
 
    #define BSLA_MAYBE_UNUSED_IS_ACTIVE 1
#elif defined(BSLS_PLATFORM_CMP_GNU) || defined(BSLS_PLATFORM_CMP_CLANG)
    #define BSLA_MAYBE_UNUSED __attribute__((__unused__))
 
    #define BSLA_MAYBE_UNUSED_IS_ACTIVE 1
#else
    #define BSLA_MAYBE_UNUSED
#endif
 
#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 ----------------------------------
 
/** @} */
/** @} */
/** @} */