Is this legal?

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2 total messages Started by Ken Rice Tue, 27 Feb 1996 02:07

#3515

Author: Ken Rice
Date: Tue, 27 Feb 1996 02:07

43 lines
1894 bytes

template < class ItemType > class T
{
public:
    T(){}
    virtual ~T(){}
    ItemType mArr;
};

void main(void)
{
    T<int>* pA = nil;
    dynamic_cast < T<int>* > (pA);
}

Our compiler reports this error:
Error   : illegal use of incomplete struct/union/class
x.cp line 12   dynamic_cast < T<int>* > (pA);

Note that T<int> is not used in a way that causes it to be instantiated until
it gets to the dynamic_cast. The april 95 draft sec 5.2.6 [expr.dynamic.cast]
says "Types shall not be defined in a dynamic_cast."

So, the question is, does using a template that has not been instantiated
before count as 'defining a type' (as the compiler seems to think), or is
the code legal?

The example can be made to compile by gratuitously declaring a variable of
type T<int> before the dynamic_cast line to force implicit instantiation,
but that seems a bit kludgy.

Thanks,
Ken Rice.

-- 
Ken Rice
rice@tiac.net
---
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Re: Is this legal?

#3529

Author: David Byrden
Date: Wed, 28 Feb 1996 00:17

30 lines
1421 bytes

>>>>>>>
void main(void)
{
    T<int>* pA = nil;
    dynamic_cast < T<int>* > (pA);
}

Our compiler reports this error:
Error   : illegal use of incomplete struct/union/class
x.cp line 12   dynamic_cast < T<int>* > (pA);
<<<<<<<<<<


  Your compiler is not in agreement with the January 1996 draft standard, 
and I quote;



5.2.6.3  If the type of [the pointer] is the same as the required result 
type........the result is v (converted if necessary).


                                        David
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