RE: [boost] BOOST_STATIC_ASSERT and template template parameters

From: Jason Shirk (jasonsh_at_[hidden])
Date: 2002-01-28 21:24:35

Unfortunately, it's the compiler, and it has nothing to do with template
template parameters.

The compiler is improperly instantiating BOOST_STATIC_ASSERT (actually
STATIC_ASSERTION_FAILURE) when the expression depends on a non-type
parameter in a less than trivial way (like T::N, for example.)

I haven't come up with a workaround.  Perhaps those more adept at
finding workarounds could offer a suggestion.

Fortunately for me, this problem doesn't reproduce in future builds of
VC.

Jason Shirk
VC++ Compiler Team

> -----Original Message-----
> From: davidbrownell98006 [mailto:david_brownell_at_[hidden]]
> Sent: Monday, January 28, 2002 5:20 PM
> To: boost_at_[hidden]
> Subject: [boost] BOOST_STATIC_ASSERT and template template parameters
> 
> I am trying to use BOOST_STATIC_ASSERT, but I think that my problem
> is either with my compiler (VC 7.0 - aka VS.NET) or my understanding
> of template template parameters.  I would like the following code to
> compile without errors.  The code is pretty straight forward, so I
> will just post it rather than trying to explain it in plain English.
> 
> Thanks in advance for your help, and please be gentle if this is
> simply a stupid question :)
> 
> David Brownell
> 
> //////////////////////////////////////////////////////////////
> //////////////////////////////////////////////////////////////
> 
> #include "boost\static_assert.hpp"
> 
> #define COMPILE_LESS_DESIRABLE_CODE     1
> 
> template <unsigned int Number>
> struct Size
> {
>     enum { SIZE = Number };
> };
> 
> template <
>             class SizeClass,
>             template <class> class APolicy
>          >
> struct AClass : public APolicy<SizeClass>
> {
> };
> 
> template <class SizeClass>
> struct PolicyNumber1
> {
> #if COMPILE_LESS_DESIRABLE_CODE
>     enum { SizeClassSize = SizeClass::SIZE };
>     BOOST_STATIC_ASSERT(SizeClassSize == 1);
> #else   //COMPILE_LESS_DESIRABLE_CODE
>     BOOST_STATIC_ASSERT(SizeClass::SIZE == 1);
> #endif  //COMPILE_LESS_DESIRABLE_CODE
> };
> 
> template <class SizeClass>
> struct PolicyNumber2
> {
> #if COMPILE_LESS_DESIRABLE_CODE
>     enum { SizeClassSize = SizeClass::SIZE };
>     BOOST_STATIC_ASSERT(SizeClassSize == 2);
> #else   //COMPILE_LESS_DESIRABLE_CODE
>     BOOST_STATIC_ASSERT(SizeClass::SIZE == 2);
> #endif  //COMPILE_LESS_DESIRABLE_CODE
> };
> 
> int main(void)
> {
>     AClass<Size<1>, PolicyNumber1>      c1;
>     AClass<Size<2>, PolicyNumber2>      c2;
>     return(true);
> }
> 
> 
> 
> 
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