Re: [boost] distance operation (24.3.4)

From: Zara (yozara_at_[hidden])
Date: 2006-03-16 00:56:32

On Wed, 15 Mar 2006 14:12:07 -0000, "John Maddock"
<john_at_[hidden]> wrote:

>> I have detected that the standard declares "distance" template at
>> 24.3.4, as taking two "InputIterator" as parameters.
<snip>
>
>It makes no difference: the function distance takes it's parameters by value 
>so the two forms:
>
>template <class InputIterator>
>typename iterator_traits<InputIterator>::difference_type
>distance(InputIterator first, InputIterator last);
>
>and
>
>template <class InputIterator>
>typename iterator_traits<InputIterator>::difference_type
>distance(InputIterator const first, InputIterator const last);
>
>are actually exactly the same function (the const declaration only affects 
>the mutability of the arguments within the scope of the function, they have 
>no effect on the function's type).
>
<...>
>
>That's unfortunately a compiler bug: the compiler is deducing the template 
>parameters for distance as "T const" rather than "T", I've worked around 
>this in the past by explicitly casting away the constantness of the 
>arguments to distance, but it's a pain to get right all over the place, just 
>to keep one broken compiler happy....
>

Is it really a bug?
AFAIK, the compiler is ordered to apply template function "distance"
on two members of the class. The function is const, so the members
must be const, in this case its final type will be "const char *
const". So the template deduced automatically will have the type
"const char * const" as "InputIterator", which is not a valid input
iterator, as it may not step forward or backward.

The compiler must be broken anyway, because changing the distance call
to the explicit distance<iterator>(...), where iterator is the type
defined within the struct (and thus, it should be "const char *") will
not work either.

Zara