Why is there no `is_complete` template in Boost.TypeTraits?

Is_Complete Template in Boost Library

While seeking an is_complete template in the Boost library, it became evident that such a template does not exist within Boost.TypeTraits. This raises questions about the rationale behind its absence and the potential design of such a template.

Consider the following code snippet:

<code class="cpp">//! Check whether type complete
template<typename T>
struct is_complete
{   
  static const bool value = ( sizeof(T) > 0 );
};

...

// use it in such a way
BOOST_STATIC_ASSERT( boost::is_complete<T>::value );</code>

This code is flawed as applying sizeof to an incomplete type is illegal. Therefore, an alternative solution is sought.

One possible approach involves the use of SFINAE. However, this poses a limitation as it cannot generally solve the problem without violating the One Definition Rule (ODR).

A platform-specific solution proposed by Alexey Malistov is available for MSVC with a slight modification:

<code class="cpp">namespace 
{
    template<class T, int discriminator>
    struct is_complete {  
      static T &amp; getT();   
      static char (&amp; pass(T))[2]; 
      static char pass(...);   
      static const bool value = sizeof(pass(getT()))==2;
    };
}
#define IS_COMPLETE(X) is_complete<X,__COUNTER__>::value</code>

Unfortunately, the use of the __COUNTER__ macro is not standardized, potentially limiting its applicability across different compilers.

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