Re: [boost] Array support [was SmartPtr (Loki) - auto_ptr/move c'tor issue]

From: Beman Dawes (bdawes_at_[hidden])
Date: 2003-02-02 20:02:11

At 04:18 PM 2/2/2003, David Abrahams wrote:

 >> In other words, there are four interface combinations:
 >>
 >>     When T is not an array && conversion to T* is not desired:
 >>
 >>         T& operator*() const;
 >>         T* operator->() const;
 >>
 >>     When T is not an array && conversion to T* is desired:
 >>
 >>         T& operator*() const;
 >>         T* operator->() const;
 >>         operator T*() const;
 >>
 >>     When T is an array && conversion to T* is not desired:
 >>
 >>         T& operator[](size_t i) const;
 >>
 >>     When T is an array && conversion to T* is desired:
 >>
 >>         operator T*() const;
 >
 >Why can't operator T*() and operator[](size_t) coexist?

They are ambiguous, or at least GCC, Intel, and Microsoft compilers think 
so, although Borland only warns and Metrowerks accepts.

The Intel error message says:

test.cpp(15): error: more than one operator "[]" matches these operands: 
built-in operator "pointer-to-object[integer]" function 
"foo<T>::operator[](unsigned int) [with T=int]" operand types are: foo<int> 
[ int ]

That being said, if size_t is changed to int, all of the above compilers 
accept the code and select the correct overload. However, both VC++ 6.0 and 
7.0 fail if the argument to [] happens to be size_t.

The only way to get it to work with both VC++ 6.0 and 7.0 is to remove the 
operator T*().

So, yes, you can get operator[] and operatorT* to co-exist, but you have to 
be very careful with parameter types. Plus you can't use operator[] and 
operatorT* together with VC++ 6.0 or 7.0. Hopefully that is fixed in 7.1, 
but I haven't tried it.

--Beman