Why is this ambiguity here?

Question

Consider I have the following minimal code:

#include 

template
struct TData
{
    typedef typename boost:         


        

Answer 1

Overload resolution is a headache. But since you stumbled on a fix (eliminate conversion of the index operand to operator[]) which is too specific to the example (literals are type int but most variables you'll be using aren't), maybe you can generalize it:

template< typename IT>
typename boost::enable_if< typename boost::is_integral< IT >::type, value_type & >::type
operator [] ( IT id ) { return data[id]; }

Unfortunately I can't test this because GCC 4.2.1 and 4.5 accept your example without complaint under --pedantic. Which really raises the question whether it's a compiler bug or not.

Also, once I eliminated the Boost dependency, it passed Comeau.