bdljsn_jsonnull.h

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/// @file bdljsn_jsonnull.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bdljsn_jsonnull.h                                                  -*-C++-*-
#ifndef INCLUDED_BDLJSN_JSONNULL
#define INCLUDED_BDLJSN_JSONNULL
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bdljsn_jsonnull bdljsn_jsonnull
/// @brief  Provide a type that represents the JSON `null` value.
/// @addtogroup bdl
/// @{
/// @addtogroup bdljsn
/// @{
/// @addtogroup bdljsn_jsonnull
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bdljsn_jsonnull-purpose"> Purpose</a>
/// * <a href="#bdljsn_jsonnull-classes"> Classes </a>
/// * <a href="#bdljsn_jsonnull-description"> Description </a>
///   * <a href="#bdljsn_jsonnull-usage"> Usage </a>
///     * <a href="#bdljsn_jsonnull-example-1-basic-syntax"> Example 1: Basic Syntax </a>
///
/// # Purpose {#bdljsn_jsonnull-purpose}
/// Provide a type that represents the JSON `null` value.
///
/// # Classes {#bdljsn_jsonnull-classes}
///
/// -  bdljsn::JsonNull: type that represents the JSON `null` value.
///
/// @see  bdljsn_json
///
/// # Description {#bdljsn_jsonnull-description}
/// This component provides a single value-semantic type,
/// `bdljsn::JsonNull`, that can represent the JSON `null` value.  This
/// provides a degenerate (extremely limited) set of the conventional
/// functionality.  Objects of this class can be:
///
/// * default constructed
/// * printed ("null" is output)
/// * compared with each other (always equal).
///
/// Significantly, there is no way to specify or change the state of these
/// objects.  Thus, each object always has the same value as the others.
///
/// Additionally, support is provided for hashing via the `hashAppend` free
/// function and also a `swap` function.
///
/// ## Usage {#bdljsn_jsonnull-usage}
///
///
/// In this section we show intended usage of this component.
///
/// ### Example 1: Basic Syntax {#bdljsn_jsonnull-example-1-basic-syntax}
///
///
/// The scenario below illustrates almost all of the supported operations on the
/// `bdljsn::JsonNull` type:
///
/// First, we create a `bdljsn::JsonNull` object:
/// @code
/// bdljsn::JsonNull a;
/// @endcode
/// Then, we examine the object's printed representation:
/// @code
/// bsl::ostringstream oss;
/// oss << a;
/// assert("null" == oss.str());
/// @endcode
/// Next, we create a second object of that class and confirm that it equals the
/// object created above.
/// @code
/// bdljsn::JsonNull b;
/// assert( (a == b));
/// assert(!(a != b));
/// @endcode
/// Finally, we confirm that swapping the two objects has no effect.
/// @code
/// swap(a, b);
/// assert(a == b);
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bdl
 * @{
 */
/** @addtogroup bdljsn
 * @{
 */
/** @addtogroup bdljsn_jsonnull
 * @{
 */
 
#include <bdlscm_version.h>
 
#include <bslh_hash.h> // `hashAppend(HASH_ALG, int)`
 
#include <bsls_compilerfeatures.h>
 
#include <bsl_iosfwd.h>
 
 
namespace bdljsn {
 
                               // ==============
                               // class JsonNull
                               // ==============
 
/// This type represents the JSON null value.  There is only 1 value of this
/// type, so all objects compare equal, hash to the same value, etc.
///
/// See @ref bdljsn_jsonnull 
class JsonNull {
 
  public:
    // CREATORS
 
    /// Create a "null" JSON respresentation.  The created object is equal
    /// to all other 'JsonNull' objects.
     JsonNull() = default;
 
    // ACCESSORS
 
    /// Write "null" to the specified output `stream`, and return a
    /// reference to `stream`.  Optionally specify an initial indentation
    /// `level`, whose absolute value is incremented recursively for nested
    /// objects.  If `level` is specified, optionally specify
    /// `spacesPerLevel`, whose absolute value indicates the number of
    /// spaces per indentation level for this and all of its nested objects.
    /// If `level` is negative, suppress indentation of the first line.  If
    /// `spacesPerLevel` is negative, format the entire output on one line,
    /// suppressing all but the initial indentation (as governed by
    /// `level`).
    bsl::ostream& print(bsl::ostream& stream,
                        int           level          = 0,
                        int           spacesPerLevel = 4) const;
};
 
// FREE OPERATORS
 
/// Return `true` (unconditionally) as the specified `lhs` and `rhs` must
/// have the same value.
bool operator==(const JsonNull& lhs, const JsonNull& rhs);
 
/// Return `false` (unconditionally) as the specified `lhs` and `rhs` cannot
/// have the different values.
bool operator!=(const JsonNull& lhs, const JsonNull& rhs);
 
/// Write "null" -- the invariant value of the specified `object` -- to the
/// specified output `stream` in a single-line format and return a reference to `stream`.  
/// 
/// \note Note that   this method has the same behavior as
/// @code
/// object.print(stream, 0, -1);
/// @endcode
bsl::ostream& operator<<(bsl::ostream& stream, const JsonNull& object);
 
// FREE FUNCTIONS
 
/// Pass the specified `object` to the specified `hashAlgorithm`.  This
/// function allows `JsonNull` objects to be hashable using `bsl::hash`. 
/// 
/// \note Note that   `object` always as the same value so, for a given state of
/// `hashAppend`, the effect of calling `hashAppend` is always the same.
template <class HASHALG>
void hashAppend(HASHALG& hashAlgorithm, const JsonNull& object);
 
/// Exchange the values of the specified `a` and `b` objects.  This
/// exception provides the no-throw exception-safety guarantee.  
/// 
/// \note Note that,   since `a` and `b` have the same value (a class invariant), this
/// operation is a no-op.
void swap(JsonNull& a, JsonNull& b);
 
                               // ===============
                               // object jsonNull
                               // ===============
 
#ifdef BSLS_COMPILERFEATURES_SUPPORT_INLINE_VARIABLES
inline constexpr JsonNull jsonNull = { };
#else
extern const     JsonNull jsonNull;
#endif
    // An object having the (singular) value of the 'JsonNull' type.
 
// ============================================================================
//                            INLINE DEFINITIONS
// ============================================================================
 
                              // --------------
                              // class JsonNull
                              // --------------
 
// CREATORS
 
}  // close package namespace
 
// FREE OPERATORS
inline
bsl::ostream& bdljsn::operator<<(bsl::ostream&           stream,
                                 const bdljsn::JsonNull& object)
{
    return object.print(stream, 0, -1);
}
 
inline
bool bdljsn::operator==(const bdljsn::JsonNull& ,
                        const bdljsn::JsonNull& )
{
    return true;
}
 
inline
bool bdljsn::operator!=(const bdljsn::JsonNull& ,
                        const bdljsn::JsonNull& )
{
    return false;
}
 
template <class HASHALG>
inline
void bdljsn::hashAppend(HASHALG& hashAlgorithm, const bdljsn::JsonNull& )
{
    using bslh::hashAppend;
    hashAppend(hashAlgorithm, -1);
}
 
inline
void bdljsn::swap(bdljsn::JsonNull& , bdljsn::JsonNull& )
{
}
 
 
 
#endif  // INCLUDED_BDLJSN_JSONNULL
 
// ----------------------------------------------------------------------------
// Copyright 2022 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 ----------------------------------
 
/** @} */
/** @} */
/** @} */