function template arg deduction with arrays

[Kyle]

I used following template function:

template<class Elem, int Size>
int tabSize( Elem (&tab)[Size] ) {
return Size;
}

tu deduce size and type of an array passed as parameter, but someone
proposed making the argument const (perhaps just out const correctnes),
and it become:

template<class Elem, int Size>
int tabSize( const Elem (&tab)[Size] ) {
return Size;
}

now, Comeau online compiler refuses to accept following code

int main() {
int tab[]={1,2,3,4,5};
tabSize( tab );
}

and this rises a question - why, is there some special rule regarding
arrays with function templates ??? (or perhaps comeau is wrong)

i managed to get rid of nontype template parameter and still get the
same error

template<class Elem>
void foo( const Elem (&tab)[5] ) {}

int main() {
int tab[5] = {1,2,3,4,5};
foo( tab );
}

"ComeauTest .c", line 6: error: no instance of function template "foo"
matches the
argument list
The argument types that you used are: (int [5])
foo( tab );
^

[Alf P. Steinbach]

Re: function template arg deduction with arrays

* Kyle:[color=blue]
> I used following template function:
>
> template<class Elem, int Size>
> int tabSize( Elem (&tab)[Size] ) {
> return Size;
> }
>
> tu deduce size and type of an array passed as parameter, but someone
> proposed making the argument const (perhaps just out const correctnes),
> and it become:
>
> template<class Elem, int Size>
> int tabSize( const Elem (&tab)[Size] ) {
> return Size;
> }
>
> now, Comeau online compiler refuses to accept following code
>
> int main() {
> int tab[]={1,2,3,4,5};
> tabSize( tab );
> }
>
> and this rises a question - why, is there some special rule regarding
> arrays with function templates ??? (or perhaps comeau is wrong)
>
> i managed to get rid of nontype template parameter and still get the
> same error
>
> template<class Elem>
> void foo( const Elem (&tab)[5] ) {}
>
> int main() {
> int tab[5] = {1,2,3,4,5};
> foo( tab );
> }
>
> "ComeauTest .c", line 6: error: no instance of function template "foo"
> matches the
> argument list
> The argument types that you used are: (int [5])
> foo( tab );
> ^[/color]

I believe this is a bug in Comeau. The code

template<class Elem, int Size>
int tabSize( const Elem (&tab)[Size] ) {
return Size;
}

int main()
{
int tab[]={1,2,3,4,5};
tabSize( tab );
}

compiles fine with MSVC 7.1 and with g++ 3.4.4.


--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
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[Maxim Yegorushkin]

Re: function template arg deduction with arrays


Alf P. Steinbach wrote:

[]
[color=blue][color=green]
> > template<class Elem>
> > void foo( const Elem (&tab)[5] ) {}
> >
> > int main() {
> > int tab[5] = {1,2,3,4,5};
> > foo( tab );
> > }
> >
> > "ComeauTest .c", line 6: error: no instance of function template "foo"
> > matches the
> > argument list
> > The argument types that you used are: (int [5])
> > foo( tab );
> > ^[/color]
>
> I believe this is a bug in Comeau. The code[/color]

So do I, because it does compile this code:

int a[2];
int const(&b)[2] = a;

IOW, it does bind a reference to an array of const to an array of
non-const.