Re: TypeTraits for Parameters
I faced a similiar problem when I wrote a template library to ease the
use of the JNI.
My solution was: Make the function's parameter types part of the class
template, providing 'void' as default types for
non-existing arguments. Then, partially specialize the class. With
that scheme, you can apply type traits to the parameters!
Here's a rough sketch, using a maximum of 2 parameters:
// Primary template, will never be used with void for A1 or A2
template<class T,class A1=void,class A2=void> class Creator<T,A1,A2>
{
public:
template<typename I> static HRESULT Create(I** ppI,
TypeTraits<A1>::ParameterType a1, TypeTraits<A2>::ParameterType a2)
{
}
};
template<class T> class Creator<T,void,void>
{
public:
template<typename I> static HRESULT Create(I** ppI)
{
}
};
template<class T,class A1> class Creator<T,A1,void>
{
public:
template<typename I> static HRESULT Create(I** ppI,
TypeTraits<A1>::ParameterType a1)
{
}
};
On 27 Mai, 09:38, jrwats <jrw...@gmail.com> wrote:
So we have this templated factory for COM objects. A simplistic view
of it would be the following:
template <class T>
class Creator
{
public:
// const& arguments
template <class I>
static HRESULT Create(I** ppI)
{
return Create(NoArg(), NoArg(), NoArg(), NoArg(), NoArg(),
NoArg(), NoArg(), NoArg(), ppI);
}
template <class TArg1, class I>
static HRESULT Create(TArg1 t1, __deref_out I** ppI)
{
return Create(t1, NoArg(), NoArg(), NoArg(), NoArg(),
NoArg(), NoArg(), NoArg(), ppI);
}
// Handle Arguments 2 - 7 as above
template <class TArg1, class TArg2, class TArg3, class TArg4,
class TArg5,
class TArg6, class TArg7, class TArg8, class I>
static HRESULT Create(TArg1 t1, TArg2 t2, TArg3 t3, TArg4 t4,
TArg5 t5,
TArg6 t6, TArg7 t7, TArg8 t8, I** ppI)
{
HRESULT hr = S_OK;
T* pT = NULL;
// Creation code here...
if (hr >= 0)
{
hr = __Init(pT, t1, t2, t3, t4, t5, t6, t7, t8);
}
else
{
return E_OUTOFMEMORY;
}
if (hr >= 0)
{
*ppI = pT;
hr = S_OK;
}
return hr;
}
template <class TArg1, class TArg2, class TArg3, class TArg4,
class TArg5,
class TArg6, class TArg7, class TArg8>
static HRESULT __Init(__in T* pT, TArg1 t1, TArg2 t2, TArg3 t3,
TArg4 t4,
TArg5 t5, TArg6 t6, TArg7 t7, TArg8 t8)
{
return pT->Initialize(t1, t2, t3, t4, t5, t6, t7, t8);
}
template <class TArg1, class TArg2, class TArg3, class TArg4,
class TArg5,
class TArg6, class TArg7>
static HRESULT __Init(__in T* pT, TArg1 t1, TArg2 t2, TArg3 t3,
TArg4 t4,
TArg5 t5, TArg6 t6, TArg7 t7, NoArg)
{
return pT->Initialize(t1, t2, t3, t4, t5, t6, t7);
}
// handle Arguments 6 - 0 via template specialization as above
};
The problem is passing in an instance of some class CFoo calls the
copy constructor. And if I make all the arguments const& then people
cannot do the following:
HRESULT (*PfnCreator)(ISomeInterface* pSomeInterface, IDesiredObject**
ppDesiredObject) =
*ComCreator<CDesiredObject>::Create;
Since the function signature is actually
HRESULT Create(ISomeInterface* const& pSomeInterface, IDesiredObject**
ppDesiredObject);
So I'd like to avoid this as I'd hate for callers to have to go do
this.
I also can't defineCreate as follows
template <class TArg1, class I>
static HRESULT Create(TypeTraits<TArg1>::ParameterType t1,
__deref_out I** ppI)
{
return Create(t1, NoArg(), NoArg(), NoArg(), NoArg(),
NoArg(), NoArg(), NoArg(), ppI);
}
As this simply can't work since template argument deduction has
already happened to determine the type of TArg1.
Are there any other solutions so this? Again I do *not* want an
ubiquitous const&.
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