smart pointers

[jwwalker]

Filament has various kinds of pointers that must be cleaned up by calling an Engine::destroy method. Making sure that such pointers get cleaned up, but not too soon, suggests to me that smart pointers should be used. It is possible to use std::shared_ptr with a deleter object passed to the constructor and reset method, but you'd have to remember to always use the deleter. Here's what I came up with. First, make a deleter object class, like:

class DestroyerByEngine
{
public:
						DestroyerByEngine( filament::Engine& inEngine );
						DestroyerByEngine( const DestroyerByEngine& inOther );
						~DestroyerByEngine() {}
	
	void				operator()( filament::VertexBuffer* vb ) const;
	void				operator()( filament::IndexBuffer* ib ) const;
	void				operator()( filament::MaterialInstance* mi ) const;
	void				operator()( filament::Texture* t ) const;
	// etc...

private:
	filament::Engine&	_engine;
};

and then define a smart pointer template:

template <typename T>
class EngineSharedPtr
{
public:
	EngineSharedPtr()
		: _engine( nullptr  ) {}

	EngineSharedPtr( const EngineSharedPtr& inOther )
		: _ptr( inOther._ptr )
		, _engine( inOther._engine ) {}

	EngineSharedPtr( T* t, filament::Engine* inEngine )
		: _ptr( t, DestroyerByEngine( *inEngine ) )
		, _engine( inEngine ) {}
	
	EngineSharedPtr& operator=( const EngineSharedPtr& inOther )
	{
		_ptr = inOther._ptr;
		_engine = inOther._engine;
		return *this;
	}
	
	T*	operator->() const noexcept { return _ptr.get(); }
	
	T*	get() const noexcept { return _ptr.get(); }
	
	void reset() noexcept
	{
		_ptr.reset();
		_engine = nullptr;
	}
	
	void reset( T* t, filament::Engine* inEngine )
	{
		_engine = inEngine;
		_ptr.reset( t, DestroyerByEngine( *_engine ) );
	}
	
private:
	std::shared_ptr< T >	_ptr;
	filament::Engine*		_engine;
};

Thoughts?

[jwwalker]

On further reflection, it might be a bit more flexible if the destroyer class were another template parameter of EngineSharedPtr. Of course you'd use it with typedefs, like

typedef EngineSharedPtr< filament::Texture, DestroyerByEngine > sharedTexture;