// bslmf_addpointer.h                                                 -*-C++-*-
#ifndef INCLUDED_BSLMF_ADDPOINTER
#define INCLUDED_BSLMF_ADDPOINTER

#include <bsls_ident.h>
BSLS_IDENT("$Id: $")

//@PURPOSE: Provide meta-function to transform a type to pointer to that type.
//
//@CLASSES:
//  bsl::add_pointer: meta-function to transform a type to a pointer type
//  bsl::add_pointer_t: alias to the return type of the `bsl::add_pointer`
//
//@SEE_ALSO: bslmf_removepointer
//
//@DESCRIPTION: This component defines a meta-function, `bsl::add_pointer`,
// that may be used to transform a type to a pointer to that type.
//
// `bsl::add_pointer` meets the requirements of the `add_pointer` template
// defined in the C++11 standard [meta.trans.ptr].
//
///Usage
///-----
// In this section we show intended use of this component.
//
///Example 1: Transform Type to Pointer Type to that Type
/// - - - - - - - - - - - - - - - - - - - - - - - - - - -
// Suppose that we want to transform a type to a pointer type to that type.
//
// First, we create two `typedef`s -- a pointer type (`MyPtrType`) and the type
// pointed to by the pointer type (`MyType`):
// ```
// typedef int   MyType;
// typedef int * MyPtrType;
// ```
// Now, we transform `MyType` to a pointer type using `bsl::add_pointer` and
// verify that the resulting type is the same as `MyPtrType`:
// ```
// assert((bsl::is_same<bsl::add_pointer<MyType>::type, MyPtrType>::value));
// ```
// Finally, if the current compiler supports alias templates C++11 feature, we
// transform `MyType` to a pointer type using `bsl::add_pointer_t` and verify
// that the resulting type is the same as `MyPtrType`:
// ```
// #ifdef BSLS_COMPILERFEATURES_SUPPORT_ALIAS_TEMPLATES
//   assert((bsl::is_same<bsl::add_pointer_t<MyType>, MyPtrType>::value));
// #endif
// ```
// Note, that the `bsl::add_pointer_t` avoids the `::type` suffix and
// `typename` prefix when we want to use the result of the `bsl::add_pointer`
// meta-function in templates.

#include <bslscm_version.h>

#include <bsls_compilerfeatures.h>
#include <bsls_platform.h>

#include <stddef.h>

#ifndef BDE_DONT_ALLOW_TRANSITIVE_INCLUDES
#include <bslmf_removereference.h>
#endif // BDE_DONT_ALLOW_TRANSITIVE_INCLUDES

namespace BloombergLP {
namespace bslmf {

/// This utility `struct` is a private implementation detail that hosts an
/// overloaded pair of functions that, through SFINAE, can determine whether
/// it is legal to form a pointer to a specified `t_TYPE`.
struct AddPointer_Compute {

    struct LargeResult {
        char d_dummy[99];
    };

    template <class t_TYPE>
    static LargeResult canFormPointer(t_TYPE *);

    template <class t_TYPE>
    static char canFormPointer(...);
};

/// For the majority of types, it is perfectly reasonable to form the type
/// `t_TYPE *`.
template <class t_TYPE,
          size_t = sizeof(AddPointer_Compute::canFormPointer<t_TYPE>(0))>
struct AddPointer_Impl {

    typedef t_TYPE *type;  // A pointer to the original 't_TYPE'.
};

/// For special cases, such as references and "abominable" functions, it is
/// not legal to form a pointer, and this parital specialization will be
/// chosen by the computed default template parameter.
template <class t_TYPE>
struct AddPointer_Impl<t_TYPE, 1u> {

    typedef t_TYPE type;  // Do not modify the type if a pointer is not valid.
};

#if defined(BSLS_PLATFORM_CMP_IBM)
template <class t_TYPE>
struct AddPointer_Impl<t_TYPE[], 1u> {
    // IBM miscomputes the SFINAE condition for arrays of unknown bound, so we
    // provide an additional partial specialization for this platform.

    typedef t_TYPE (*type)[];     // A pointer to the original 't_TYPE[]'.
};
#endif

}  // close package namespace
}  // close enterprise namespace

namespace bsl {

                         // ==================
                         // struct add_pointer
                         // ==================

/// This `struct` template implements the `add_pointer` meta-function
/// defined in the C++11 standard [meta.trans.ptr], providing an alias,
/// `type`, that returns the result.  If the (template parameter) `t_TYPE`
/// is not a reference type, then `type` is an alias to a pointer type that
/// points to `t_TYPE`; otherwise, `type` is an alias to a pointer type that
/// points to the type referred to by the reference `t_TYPE`, unless it is
/// not legal to form such a pointer type, in which case `type` is an alias
/// for `t_TYPE`.
template <class t_TYPE>
struct add_pointer {

    /// This `typedef` is an alias to a pointer type that points to the
    /// (template parameter) `t_TYPE` if it is not a reference type;
    /// otherwise, this `typedef` is an alias to a pointer type that points
    /// to the type referred to by the reference `t_TYPE`.
    typedef typename BloombergLP::bslmf::AddPointer_Impl<t_TYPE>::type type;
};

/// If we can form a reference to `t_TYPE`, then we can also form a pointer
/// to it.  In particular, we know that it is not `void` (which should still
/// work) or an "abominable" function type with a trailing cv-qualifier.
/// Note that this partial specialization is necessary to avoid falling into
/// degenerate (non-compiling) cases in the implementation meta-program.
template <class t_TYPE>
struct add_pointer<t_TYPE&> {

    typedef t_TYPE * type;
};

#if defined(BSLS_COMPILERFEATURES_SUPPORT_RVALUE_REFERENCES)
/// If we can form a reference to `t_TYPE`, then we can also form a pointer
/// to it.  In particular, we know that it is not `void` (which should still
/// work) or an "abominable" function type with a trailing cv-qualifier.
/// Note that this partial specialization is necessary to avoid falling into
/// degenerate (non-compiling) cases in the implementation meta-program.
template <class t_TYPE>
struct add_pointer<t_TYPE&&> {

    typedef t_TYPE * type;
};
#endif

#ifdef BSLS_COMPILERFEATURES_SUPPORT_ALIAS_TEMPLATES

//ALIASES

/// `add_pointer_t` is an alias to the return type of the `bsl::add_pointer`
/// meta-function.  Note, that the `remove_pointer_t` avoids the `::type`
/// suffix and `typename` prefix when we want to use the result of the
/// meta-function in templates.
template <class t_TYPE>
using add_pointer_t = typename add_pointer<t_TYPE>::type;

#endif  // BSLS_COMPILERFEATURES_SUPPORT_ALIAS_TEMPLATES

}  // close namespace bsl

#endif

// ----------------------------------------------------------------------------
// Copyright 2017 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 ----------------------------------
