Problem with dll and BOOST_STATIC_ASSERT

Frank

4 Nov 2005 4 Nov '05

12:39 a.m.

I have the following code ( very simplified but compilable) // =========== start snip =============================== /// ======= in hpp ============ #include template class Vector { public: Vector(void) {/*init code omitted*/} Vector(const Vector& v) {/* ctor code omitted */} //===================================================== // some ctors for small DIM's // will cause compile time errors if DIM != # of args //===================================================== #ifdef enable_small_dim_ctor explicit Vector( T x ) { BOOST_STATIC_ASSERT(DIM==1); data_[0]=x; } Vector( T x, T y ) { BOOST_STATIC_ASSERT(DIM==2); data_[0]=x; data_[1]=y; } Vector( T x, T y, T z ) { BOOST_STATIC_ASSERT(DIM==3); data_[0]=x; data_[1]=y; data_[2]=z; } #endif private: T data_[DIM]; }; template <typename T> class Vector3 : public Vector { public: Vector3(){}; Vector3 Normal() const; }; //==================== in cpp ================= // provide implementation of Normal template <typename T> Vector3<T> Vector3<T>::Normal() const { Vector3 n; return n; } // explicit instantiation of the normal method #ifdef try_export // causes error STATIC_ASSERTION_FAILURE template class __declspec(dllexport) Vector3<double> Vector3<double>::Normal() const; #else //OK template class Vector3<double> Vector3<double>::Normal() const; #endif // ============== end snip =============================== I 'm trying to put the implementation into a dll and mark the explicit instantiation of Normal as exported with the following results: 1) With the small_dim_ctor's enabled I get the static assertion when marked for export 2) With the small_dim_ctor's enabled everything is ok when not marked for export 3) With the small_dim_ctor's disabled everything is ok regardless of export marking 4) If I comment out the BOOST_STATIC_ASSERT and build my app with export enabled I can use the resulting dll without any problems I'm thinking that marking for export is somewhow generating an implicit conversion somewhere but I don't know how. Using VStudio .Net 2003. Any help is appreciated. Thanks Frank

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João Abecasis

4 Nov 4 Nov

10 a.m.

Frank wrote:

...

I 'm trying to put the implementation into a dll and mark the explicit instantiation of Normal as exported with the following results: 1) With the small_dim_ctor's enabled I get the static assertion when marked for export 2) With the small_dim_ctor's enabled everything is ok when not marked for export 3) With the small_dim_ctor's disabled everything is ok regardless of export marking 4) If I comment out the BOOST_STATIC_ASSERT and build my app with export enabled I can use the resulting dll without any problems

I'm thinking that marking for export is somewhow generating an implicit conversion somewhere but I don't know how.

I suppose marking the class for export could instantiate all member functions and constructors and thus trigger the static assertions. Have you considered using boost::enable_if instead of BOOST_STATIC_ASSERT? Regards, João Abecasis

Frank

9:19 p.m.

New subject: [Boost-users] Problem with dll and BOOST_STATIC_ASSERT

João Abecasis writes:

...

Frank wrote:

...
I 'm trying to put the implementation into a dll and mark the explicit instantiation of Normal as exported with the following results: 1) With the small_dim_ctor's enabled I get the static assertion when marked for export 2) With the small_dim_ctor's enabled everything is ok when not marked for export 3) With the small_dim_ctor's disabled everything is ok regardless of export marking 4) If I comment out the BOOST_STATIC_ASSERT and build my app with export enabled I can use the resulting dll without any problems

I'm thinking that marking for export is somewhow generating an implicit conversion somewhere but I don't know how.

I suppose marking the class for export could instantiate all member functions and constructors and thus trigger the static assertions.

Have you considered using boost::enable_if instead of BOOST_STATIC_ASSERT?

Regards,

João Abecasis

I thought I was only marking the explicit specialization of a single method ( eg Normal) for exporting or maybe it's because its not possible to specialize just one method.? After reading your reply I had a look at enable_if but I couldn't figure a way to test the DIM ie template <typename T> explicit Vector( T x, typename boost::enable_if< DIM==1, void*>::type = 0 ) { data_[0]=x; } but I'm not sure I understand how to use it and am still surfing for examples. Thanks for the help. Frank

John Maddock

10:35 a.m.

...

I 'm trying to put the implementation into a dll and mark the explicit instantiation of Normal as exported with the following results: 1) With the small_dim_ctor's enabled I get the static assertion when marked for export 2) With the small_dim_ctor's enabled everything is ok when not marked for export 3) With the small_dim_ctor's disabled everything is ok regardless of export marking 4) If I comment out the BOOST_STATIC_ASSERT and build my app with export enabled I can use the resulting dll without any problems

I'm thinking that marking for export is somewhow generating an implicit conversion somewhere but I don't know how.

Unfortunately, when you explicitly instantiate a template every non-template member function gets instantiated, and that triggers the static asserts. The only workarounds I can see are: 1) Use regular asserts whenever the class is being exported rather than static asserts. 2) Use partial template specialisations for the N = 1, 2 or 3 cases and give them different constructors (no need to static asserts then). 3) Use template constructors instead: template <class U> explicit Vector( U x ) { BOOST_STATIC_ASSERT(DIM==1); data_[0]=x; } Hope this helps, John.

Frank

7:47 p.m.

New subject: [Boost-users] Problem with dll and BOOST_STATIC_ASSERT

John Maddock writes:

...

...
I 'm trying to put the implementation into a dll and mark the explicit instantiation of Normal as exported with the following results: 1) With the small_dim_ctor's enabled I get the static assertion when marked for export 2) With the small_dim_ctor's enabled everything is ok when not marked for export 3) With the small_dim_ctor's disabled everything is ok regardless of export marking 4) If I comment out the BOOST_STATIC_ASSERT and build my app with export enabled I can use the resulting dll without any problems

I'm thinking that marking for export is somewhow generating an implicit conversion somewhere but I don't know how.

Unfortunately, when you explicitly instantiate a template every non-template member function gets instantiated, and that triggers the static asserts.

The only workarounds I can see are:

1) Use regular asserts whenever the class is being exported rather than static asserts. 2) Use partial template specialisations for the N = 1, 2 or 3 cases and give them different constructors (no need to static asserts then). 3) Use template constructors instead:

template <class U> explicit Vector( U x ) { BOOST_STATIC_ASSERT(DIM==1); data_[0]=x; }

Hope this helps, John.

Frank

9:21 p.m.

New subject: [Boost-users] Problem with dll and BOOST_STATIC_ASSERT

Sorry. Posted to wrong reply. Frank

Frank

7:58 p.m.

New subject: [Boost-users] Problem with dll and BOOST_STATIC_ASSERT

John Maddock writes:

...

...
I 'm trying to put the implementation into a dll and mark the explicit instantiation of Normal as exported with the following results: 1) With the small_dim_ctor's enabled I get the static assertion when marked for export 2) With the small_dim_ctor's enabled everything is ok when not marked for export 3) With the small_dim_ctor's disabled everything is ok regardless of export marking 4) If I comment out the BOOST_STATIC_ASSERT and build my app with export enabled I can use the resulting dll without any problems

I'm thinking that marking for export is somewhow generating an implicit conversion somewhere but I don't know how.

Unfortunately, when you explicitly instantiate a template every non-template member function gets instantiated, and that triggers the static asserts.

The only workarounds I can see are:

1) Use regular asserts whenever the class is being exported rather than static asserts. 2) Use partial template specialisations for the N = 1, 2 or 3 cases and give them different constructors (no need to static asserts then). 3) Use template constructors instead:

template <class U> explicit Vector( U x ) { BOOST_STATIC_ASSERT(DIM==1); data_[0]=x; }

Hope this helps, John.

Soln 1) I was trying for compile time checks but will fall back to this Soln 2) I understood partial specialization wasn't supported in VStudio but I might do this for float, double and dim 1-4; I had started to do something similar by deriving Vector3<T> template from Vector when I ran into the trouble. Soln 3) I like this one but haven't made it work yet. It succeeds if I export the specialized Vector::Normal() but not if I export Vector3<T>::Normal () but i'm working on it ;-) Thanks for the help Frank

John Maddock

5 Nov 5 Nov

11:55 a.m.

...

Soln 1) I was trying for compile time checks but will fall back to this

Understood. It's a weird error: I don't believe that the compiler should be instantiating those methods at all, but <shrug>.

...

Soln 2) I understood partial specialization wasn't supported in VStudio but I might do this for float, double and dim 1-4; I had started to do something similar by deriving Vector3<T> template from Vector when I ran into the trouble.

Partial specialisation works just fine in Visual Studio 2003 (VC7.1 and later).

...

Soln 3) I like this one but haven't made it work yet. It succeeds if I export the specialized Vector::Normal() but not if I export Vector3<T>::Normal () but i'm working on it ;-)

Your right, I've just tried it out, and it leads to even stranger errors: the template members get instantiated with some really strange argument types, I've no idea what's going on there at present. John.

Frank

7 Nov 7 Nov

7:51 p.m.

New subject: [Boost-users] Problem with dll and BOOST_STATIC_ASSERT

John Maddock writes:

...

It's a weird error: I don't believe that the compiler should be instantiating those methods at all, but <shrug>.

I don't have access to any other compilers so don't know if it's a VStudio problem.

...

Partial specialisation works just fine in Visual Studio 2003 (VC7.1 and later).

I could never get it to work but it may be my lack of understanding even tho I looked at dozens of examples.

...

...
Soln 3) I like this one but haven't made it work yet. It succeeds if I export the specialized Vector::Normal() but not if I export Vector3<T>::Normal () but i'm working on it

Your right, I've just tried it out, and it leads to even stranger errors: the template members get instantiated with some really strange argument types, I've no idea what's going on there at present.

I converted my template hierarchy to get rid of the Vector3<T> derivation and added the "low Dim" ctor's to the Vector template. But I couldn't use the template <typename U> member templates approach because I have other ctor's with 2 parameters and the wrong one was getting used. ie: i have a ctor: Vector( Point from, Point to){} when I write Vector v(Point(...), Point(...) ) "it" would try to construct v using template <typename U> Vector( U x, U y ){...} I've essentially given up for now and resorted to runtime check using BOOST_ASSERT. Thanks for the assistance Frank

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Frank
John Maddock
João Abecasis