staticInterface.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_PLUG_STATIC_INTERFACE_H
#define PXR_BASE_PLUG_STATIC_INTERFACE_H
 
 
#include "pxr/pxr.h"
#include "pxr/base/plug/api.h"
 
#include <atomic>
#include <type_traits>
#include <typeinfo>
 
PXR_NAMESPACE_OPEN_SCOPE
 
// Base class for common stuff.
class Plug_StaticInterfaceBase {
public:
    bool IsInitialized() const
    {
        return _initialized;
    }
 
#if !defined(doxygen)
    typedef void* Plug_StaticInterfaceBase::*UnspecifiedBoolType;
#endif
 
protected:
    PLUG_API
    void _LoadAndInstantiate(const std::type_info& type) const;
 
protected:
    // POD types only!
    mutable std::atomic<bool> _initialized;
    mutable void* _ptr;
};
 
template <class Interface>
class PlugStaticInterface : private Plug_StaticInterfaceBase {
public:
    static_assert(std::is_abstract<Interface>::value,
                  "Interface type must be abstract.");
 
    typedef PlugStaticInterface<Interface> This;
 
    using Plug_StaticInterfaceBase::IsInitialized;
 
    operator UnspecifiedBoolType() const
    {
        return _GetPtr() ? &This::_ptr : nullptr;
    }
 
    bool operator!() const
    {
        return !*this;
    }
 
    Interface* Get() const
    {
        return _GetPtr();
    }
 
    Interface* operator->() const
    {
        return _GetPtr();
    }
 
    Interface& operator*() const
    {
        return *_GetPtr();
    }
 
private:
    Interface* _GetPtr() const
    {
        if (!_initialized) {
            _LoadAndInstantiate(typeid(Interface));
        }
 
        // XXX: We must assume _ptr has the right type since we have
        //      no common base class to dynamic_cast<> from.
        return static_cast<Interface*>(_ptr);
    }
};
 
PXR_NAMESPACE_CLOSE_SCOPE
 
#endif // PXR_BASE_PLUG_STATIC_INTERFACE_H