weakPtrFacade.h

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//
// Copyright 2016 Pixar
//
// Licensed under the terms set forth in the LICENSE.txt file available at
// https://openusd.org/license.
//
#ifndef PXR_BASE_TF_WEAK_PTR_FACADE_H
#define PXR_BASE_TF_WEAK_PTR_FACADE_H

#include "pxr/pxr.h"

#include "pxr/base/tf/diagnostic.h"
#include "pxr/base/tf/hash.h"
#include "pxr/base/tf/refPtr.h"
#include "pxr/base/tf/weakBase.h"

#include "pxr/base/arch/demangle.h"

#include <type_traits>

PXR_NAMESPACE_OPEN_SCOPE

template <class U> class TfRefPtr;

template <template <class> class PtrTemplate, class DataType>
class TfWeakPtrFacade;

/// \class TfWeakPtrFacadeAccess
///
/// This access class is befriended by \c TfWeakPtrFacade -derived classes to
/// grant \c TfWeakPtrFacade access to specific internal functions provided by
/// the derived classes.
class TfWeakPtrFacadeAccess {
public:
    template <template <class> class PtrTemplate, class DataType>
    friend class TfWeakPtrFacade;

    template <class Facade>
    static typename Facade::DataType *FetchPointer(Facade const &f) {
        return f._FetchPointer();
    }

    template <class Facade>
    static void const *GetUniqueIdentifier(Facade const &f) {
        return f._GetUniqueIdentifier();
    }

    template <class Facade>
    static void EnableExtraNotification(Facade const &f) {
        return f._EnableExtraNotification();
    }

    template <class Facade>
    static bool IsInvalid(Facade const &f) {
        return f._IsInvalid();
    }

private:
    TfWeakPtrFacadeAccess();
};

template <template <class> class X, class Y>
Y *get_pointer(TfWeakPtrFacade<X, Y> const &p) {
    return TfWeakPtrFacadeAccess::FetchPointer(p);
}

// Common base class, used to identify subtypes in enable_if expressions.
class TfWeakPtrFacadeBase {};

template <template <class> class PtrTemplate, class Type>
class TfWeakPtrFacade : public TfWeakPtrFacadeBase {

public:

    friend class TfWeakPtrFacadeAccess;
    
    typedef Type DataType;
    typedef PtrTemplate<DataType> Derived;
    typedef TfWeakPtrFacadeAccess Access;

    typedef Type element_type;
    
    template <class Other>
    bool operator == (PtrTemplate<Other> const &p) const {
        if (false)
            return _FetchPointer() == TfWeakPtrFacadeAccess::FetchPointer(p);
        return GetUniqueIdentifier() == p.GetUniqueIdentifier();
    }

    template <class Other>
    bool operator != (PtrTemplate<Other> const &p) const {
        return !(*this == p);
    }

    template <class T>
    bool operator == (TfRefPtr<T> const &p) const {
        if (!GetUniqueIdentifier())
            return !p;
        DataType *ptr = _FetchPointer();
        return ptr && ptr == get_pointer(p);
    }

    template <class T>
    bool operator != (TfRefPtr<T> const &p) const {
        return !(*this == p);
    }

    template <class T>
    friend bool operator == (const TfRefPtr<T>& p1, Derived const &p2) {
        return p2 == p1;
    }

    template <class T>
    friend bool operator != (const TfRefPtr<T>& p1, Derived const &p2) {
        return !(p1 == p2);
    }

    template <class Other>
    bool operator < (PtrTemplate<Other> const &p) const {
        if (false)
            return _FetchPointer() < TfWeakPtrFacadeAccess::FetchPointer(p);
        return GetUniqueIdentifier() < p.GetUniqueIdentifier();
    }

    template <class Other>
    bool operator > (PtrTemplate<Other> const &p) const {
        return !(*this < p) && !(*this == p);
    }

    template <class Other>
    bool operator <= (PtrTemplate<Other> const &p) const {
        return (*this < p) || (*this == p);
    }

    template <class Other>
    bool operator >= (PtrTemplate<Other> const &p) const {
        return !(*this < p);
    }

    using UnspecifiedBoolType = DataType * (TfWeakPtrFacade::*)(void) const;

    operator UnspecifiedBoolType () const {
        return _FetchPointer() ? &TfWeakPtrFacade::_FetchPointer : nullptr;
    }

    bool operator ! () const {
        return !(bool(*this));
    }

    template <class T>
    bool PointsTo(T const &obj) const {
        return _FetchPointer() == &obj;
    }

    /// Return true if this object points to an object of type \a T.  \a T
    /// must either be the same as or a base class of \a DataType or DataType
    /// must be polymorphic.
    template <class T>
    bool PointsToA() const {
        return dynamic_cast<T *>(_FetchPointer());
    }

    bool IsInvalid() const {
        return Access::IsInvalid(_Derived());
    }
    
    void const *GetUniqueIdentifier() const {
        return Access::GetUniqueIdentifier(_Derived());
    }

    TfWeakBase const *GetWeakBase() const {
        return &_Derived()->__GetTfWeakBase__();
    }

    void EnableExtraNotification() const {
        Access::EnableExtraNotification(_Derived());
    }
    
    DataType *operator -> () const {
        DataType *ptr = _FetchPointer();
        if (ptr) {
            return ptr;
        }
        Tf_PostNullSmartPtrDereferenceFatalError(
            TF_CALL_CONTEXT, typeid(Derived).name());
    }

    DataType &operator * () const {
        return * operator->();
    }

    /// Reset this pointer to point at no object. Equivalent to assignment
    /// with \a TfNullPtr.
    void Reset() {
        _Derived() = TfNullPtr;
    }
    
private:

    friend std::type_info const &TfTypeid(Derived const &p) {
        if (ARCH_UNLIKELY(!p))
            TF_FATAL_ERROR("Called TfTypeid on invalid %s",
                           ArchGetDemangled(typeid(Derived)).c_str());
        return typeid(*get_pointer(p));
    }

    DataType *_FetchPointer() const {
        return Access::FetchPointer(_Derived());
    }

    Derived &_Derived() {
        return static_cast<Derived &>(*this);
    }

    Derived const &_Derived() const {
        return static_cast<Derived const &>(*this);
    }
            
};


/// \section nullptr comparisons
///@{
///
/// These are provided both to avoid ambiguous overloads due to
/// TfWeakPtrFacade::Derived comparisons with TfRefPtr and because implicitly
/// converting a nullptr to a TfWeakPtrFacade-derived type can add an unknown
/// amount of overhead.
///

template <template <class> class X, class Y>
inline bool operator== (TfWeakPtrFacade<X, Y> const &p, std::nullptr_t)
{
    return !p;
}
template <template <class> class X, class Y>
inline bool operator== (std::nullptr_t, TfWeakPtrFacade<X, Y> const &p)
{
    return !p;
}

template <template <class> class X, class Y>
inline bool operator!= (TfWeakPtrFacade<X, Y> const &p, std::nullptr_t)
{
    return !(p == nullptr);
}
template <template <class> class X, class Y>
inline bool operator!= (std::nullptr_t, TfWeakPtrFacade<X, Y> const &p)
{
    return !(nullptr == p);
}

template <template <class> class X, class Y>
inline bool operator< (TfWeakPtrFacade<X, Y> const &p, std::nullptr_t)
{
    return std::less<void const *>()(p.GetUniqueIdentifier(), nullptr);
}
template <template <class> class X, class Y>
inline bool operator< (std::nullptr_t, TfWeakPtrFacade<X, Y> const &p)
{
    return std::less<void const *>()(nullptr, p.GetUniqueIdentifier());
}

template <template <class> class X, class Y>
inline bool operator<= (TfWeakPtrFacade<X, Y> const &p, std::nullptr_t)
{
    return !(nullptr < p);
}
template <template <class> class X, class Y>
inline bool operator<= (std::nullptr_t, TfWeakPtrFacade<X, Y> const &p)
{
    return !(p < nullptr);
}

template <template <class> class X, class Y>
inline bool operator> (TfWeakPtrFacade<X, Y> const &p, std::nullptr_t)
{
    return nullptr < p;
}
template <template <class> class X, class Y>
inline bool operator> (std::nullptr_t, TfWeakPtrFacade<X, Y> const &p)
{
    return p < nullptr;
}

template <template <class> class X, class Y>
inline bool operator>= (TfWeakPtrFacade<X, Y> const &p, std::nullptr_t)
{
    return !(p < nullptr);
}
template <template <class> class X, class Y>
inline bool operator>= (std::nullptr_t, TfWeakPtrFacade<X, Y> const &p)
{
    return !(nullptr < p);
}

///@}

template <class ToPtr, template <class> class X, class Y>
ToPtr TfDynamic_cast(TfWeakPtrFacade<X, Y> const &p) {
    return ToPtr(dynamic_cast<typename ToPtr::DataType *>
                 (get_pointer(p)));
}

template <class ToPtr, template <class> class X, class Y>
ToPtr TfSafeDynamic_cast(TfWeakPtrFacade<X, Y> const &p) {
    return ToPtr(TfSafeDynamic_cast<typename ToPtr::DataType *>
                 (get_pointer(p)));
}

template <class ToPtr, template <class> class X, class Y>
ToPtr TfStatic_cast(TfWeakPtrFacade<X, Y> const &p) {
    return ToPtr(static_cast<typename ToPtr::DataType *>
                 (get_pointer(p)));
}

template <class ToPtr, template <class> class X, class Y>
ToPtr TfConst_cast(TfWeakPtrFacade<X, Y> const &p) {
    return ToPtr(const_cast<typename ToPtr::DataType *>
                 (get_pointer(p)));
}

//
// This is the implementation; the declaration and doxygen
// is in refPtr.h.
//
// If _remnant itself is NULL, then wp doesn't point to anything.
//

template <class T>
template <template <class> class X, class U>
inline TfRefPtr<T>::TfRefPtr(const TfWeakPtrFacade<X, U>& p,
                             typename std::enable_if<
                                 std::is_convertible<U*, T*>::value
                             >::type *)
    : _refBase(get_pointer(p))
{
    _AddRef();
    Tf_RefPtrTracker_New(this, _refBase, _NullT);
}

//
// See typeFunctions.h for documention.
//
template <template <class> class Ptr, class T>
struct TfTypeFunctions<Ptr<T>,
                       std::enable_if_t<
                           std::is_base_of<TfWeakPtrFacadeBase, Ptr<T>>::value
                       >>
{
    static T* GetRawPtr(const Ptr<T>& t) {
        return get_pointer(t);
    }

    static Ptr<T> ConstructFromRawPtr(T* ptr) {
        return Ptr<T>(ptr);
    }

    static bool IsNull(const Ptr<T>& t) {
        return !t;
    }

    static void Class_Object_MUST_Be_Passed_By_Address() { }
    static void Class_Object_MUST_Not_Be_Const() { }
};

template <template <class> class Ptr, class T>
struct TfTypeFunctions<Ptr<const T>,
                       std::enable_if_t<
                           std::is_base_of<TfWeakPtrFacadeBase, Ptr<const T>>::value
                       >>
{
    static const T* GetRawPtr(const Ptr<const T>& t) {
        return get_pointer(t);
    }

    static Ptr<const T> ConstructFromRawPtr(const T* ptr) {
        return Ptr<const T>(ptr);
    }

    static bool IsNull(const Ptr<const T>& t) {
        return !t;
    }

    static void Class_Object_MUST_Be_Passed_By_Address() { }
};

// TfHash support.
template <class HashState, template <class> class X, class T>
inline void
TfHashAppend(HashState &h, TfWeakPtrFacade<X, T> const &ptr)
{
    return h.Append(ptr.GetUniqueIdentifier());
}

// Extend boost::hash to support TfWeakPtrFacade.
template <template <class> class X, class T>
inline size_t
hash_value(TfWeakPtrFacade<X, T> const &ptr)
{
    return TfHash()(ptr);
}

PXR_NAMESPACE_CLOSE_SCOPE

#endif // PXR_BASE_TF_WEAK_PTR_FACADE_H