Subscript operator issues

[mSkull]

Hi,


I've made a class that inherits std::vector, to make it more like C#'s List.
But the subscript operator is given me trouble, that I can't figure out.
Especially as the code worked fine in my test project.

From List.h

template<class T> class List : protected std::vector<T>
{
/* unimportant stuff */

T &operator[]( const int i )
{
assert( i >= 0 && i < Count() );
return vector::operator[]( i );
}
};


And this where I'm getting the error:
error C2678: binary '[' : no operator found which takes a left-hand operand of type 'const List<Matrix4>' (or there is no acceptable conversion)

float *RenderObject::TransformData( int index ) const
{
assert( index < transforms.Count() );
return (float*)&transforms[index];
}

I'm not getting this in my test project. How come?

[Peter87]

You get an error because you have not mentioned the template argument of vector.

return vector<T>::operator[]( i );

Template code is usually not instantiated until you use it. Your test program probably didn't use the List<T>::operator[] so the code in that function was never fully evaluated.

[mSkull]

I've unfortunately already tried this, and still been getting the same error. The test program does actually use the [] operator. I delibrately changed a section of the code there to do so, but still not having that issue.

From the test program
void Display( List<Item> list )
{
cout
<< "# Contents" << endl
<< "----------" << endl;
for( int i = 0; i < list.Count(); i++ )
{
cout << i << " " << list[ i ].Name() << endl;
}
cout << endl;
}

[JLBorges]

#include <iostream>
#include <vector>
#include <cassert>
#include <iostream>

template < typename T > struct ArrayList : private std::vector<T>
{
    using base = std::vector<T> ;
    using base::base ;
    using size_type = typename base::size_type ;
    using base::size ;
    using base::begin ;
    using base::end ;
    // etc. etc.

    typename base::reference operator[] ( size_type pos )
    {
        assert( pos < base::size() ) ;
        return base::at(pos) ; // bound-checked access; may throw std::out_of_range
    }

    typename base::const_reference operator[] ( size_type pos ) const
    {
        assert( pos < base::size() ) ;
        return base::at(pos) ; // bound-checked access; may throw std::out_of_range
    }
};

int main()
{
    ArrayList<int> a { 0, 1, 2, 3, 4, 5 } ;
    const ArrayList<int>& ca = a ;
    assert( a[2] == 2 && ca[3] == 3 ) ;

    for( std::size_t i = 0 ; i < a.size() ; ++i ) a[i] *= i ;

    for( int v : ca ) std::cout << v << ' ' ;
    std::cout << '\n' ;
}

http://coliru.stacked-crooked.com/a/ce49316a1df8f9c1

[mSkull]

Thank you, that got it working