bsla_used.h

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/// @file bsla_used.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bsla_used.h                                                        -*-C++-*-
#ifndef INCLUDED_BSLA_USED
#define INCLUDED_BSLA_USED
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bsla_used bsla_used
/// @brief  Provide a macro to prevent elision of unused entities.
/// @addtogroup bsl
/// @{
/// @addtogroup bsla
/// @{
/// @addtogroup bsla_used
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bsla_used-purpose"> Purpose</a>
/// * <a href="#bsla_used-macros"> Macros </a>
/// * <a href="#bsla_used-description"> Description </a>
///   * <a href="#bsla_used-macro-reference"> Macro Reference </a>
///   * <a href="#bsla_used-usage"> Usage </a>
///     * <a href="#bsla_used-example-1-unused-variables"> Example 1: Unused Variables </a>
///     * <a href="#bsla_used-example-2-unused-functions"> Example 2: Unused Functions </a>
///
/// # Purpose {#bsla_used-purpose}
/// Provide a macro to prevent elision of unused entities.
///
/// # Macros {#bsla_used-macros}
///
/// -  BSLA_USED:           emit annotated entity even if not referenced
/// -  BSLA_USED_IS_ACTIVE: defined if `BSLA_USED` is active
///
/// @see  bsla_annotations
///
/// # Description {#bsla_used-description}
/// This component provides a preprocessor macro that will
/// guarantee the emission of a local function, type, or variable whether it is
/// used or not.
///
/// ## Macro Reference {#bsla_used-macro-reference}
///
///
///  `BSLA_USED`:
///       This annotation indicates that the so-annotated function, variable, or
///       type must be emitted even if it appears that it is not referenced.
/// 
///  `BSLA_USED_IS_ACTIVE`:
///      The macro `BSLA_USED_IS_ACTIVE` is defined if `BSLA_USED` expands to
///      something with the desired effect; otherwise `BSLA_USED_IS_ACTIVE` is
///      not defined and `BSLA_USED` expands to nothing.
///
/// ## Usage {#bsla_used-usage}
///
///
/// This section illustrates intended use of this component.
///
/// ### Example 1: Unused Variables {#bsla_used-example-1-unused-variables}
///
///
/// First, we declare two unused static variables, one marked `BSLA_UNUSED` and
/// the other marked `BSLA_USED`:
/// @code
/// static
/// int usage_UNUSED_variable_no_warning BSLA_UNUSED;
///
/// static
/// int usage_USED_variable_no_warning BSLA_USED;
/// @endcode
/// Finally, if we compile with clang and go into the debugger and stop in
/// `main`, which is in the same file and from which both variables are visible,
/// we observe that the variable marked `BSLA_UNUSED` cannot be accessed, but
/// the variable marked `BSLA_USED` can.
///
/// ### Example 2: Unused Functions {#bsla_used-example-2-unused-functions}
///
///
/// First, declare two unused static functions, one marked `BSLA_UNUSED` and one
/// marked `BSLA_USED`:
/// @code
/// /// Print the specified 'woof'.
/// static
/// void usage_UNUSED_function_no_warning(int woof) BSLA_UNUSED;
///
/// static
/// void usage_UNUSED_function_no_warning(int woof)
/// {
///     printf("%d\n", woof);
/// }
///
/// /// Print the specified 'woof'.
/// static
/// void usage_USED_function_no_warning(int woof) BSLA_USED;
///
/// static
/// void usage_USED_function_no_warning(int woof)
/// {
///     printf("%d\n", woof);
/// }
/// @endcode
/// Finally, if we compile with clang and go into the debugger, we find that we
/// can put a breakpoint in the function marked `BSLA_USED`, but not in the
/// function marked `BSLA_UNUSED`.
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bsla
 * @{
 */
/** @addtogroup bsla_used
 * @{
 */
 
#include <bsls_platform.h>
 
// Note that we could conceivably migrate this to use '[[maybe_unused]]' when
// available, but that has more specific constraints over where it can be
// syntactically placed than the older vendor annotations.
 
                       // =============================
                       // Checks for Pre-Defined macros
                       // =============================
 
#if defined(BSLA_USED)
#error BSLA_USED is already defined!
#endif
 
#if defined(BSLA_USED_IS_ACTIVE)
#error BSLA_USED_IS_ACTIVE is already defined!
#endif
 
                       // =========================
                       // Set macros as appropriate
                       // =========================
 
#if defined(BSLS_PLATFORM_CMP_GNU) || defined(BSLS_PLATFORM_CMP_CLANG)
    #define BSLA_USED       __attribute__((__used__))
 
    #define BSLA_USED_IS_ACTIVE 1
#else
    #define BSLA_USED
#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 ----------------------------------
 
/** @} */
/** @} */
/** @} */