50876cc6   
   From: daniel.kruegler@googlemail.com   
      
   Am 09.05.2012 21:26, schrieb PiotrN:   
   > Two questions:   
   >     1)  Why I cannot call destructor for builtin types like int:   
   >             int a;   
   >             int* p = new (&a) int(7);   
   >             p->~int();   
   >   
   > I found in the NET that standard says: "The notation for explicit call   
   > of a destructor can be used for any scalar type name. Allowing this   
   > makes it possible to write code without having to know if a destructor   
   > exists for a given type. "   
      
   Yes, this is roughly the rationale for it: To be able to write generic   
   code without much trickery to discriminate scalar types from class   
   types. The more precise rule is that the pseudo-destructor name is valid   
   for scalar types only, if these are provided as /type-name/ (like a   
   typedef) or a decltype-specifier (like: decltype(0)).   
      
   > And typedef int is "scalar type name" but int is not - so it works the   
   > following:   
   >           typedef int INT;   
   >           p->~INT();   
   > Why standard does allow calling destructor on typedef (and template   
   > typename) - but it has objections to plain type? Is there any   
   > rationale for this?   
      
   Only a weak one: Once you are in non-template code, you have knowledge   
   of the specific type, so why bothering with writing a no-op? This *is*   
   really a weak argument, because you have the same problem once you would   
   try to write a generic macro. In other words: I wish, we would not have   
   this constraint to support the pseudo-destructor only for type-names and   
   decltype-specifiers when we have a non-class type.   
      
   >    2) Why C++ (gcc-4.3.4) has objections to this syntax:   
   >   
   >       p->std::~string();   
   >   
   > of course this works well:   
   >   
   >     using namespace std;   
   >     p->~string();   
      
   You can write this as:   
      
   p->std::string::~string();   
      
   HTH & Greetings from Bremen,   
      
   Daniel Krügler   
      
      
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