Question

I want to create a simple integer range checker and converter using c++ templates.
The code looks like this:

// D is the "destination" type and S the "source" type
template <class D, class S>
inline D SafeConvert( S value );

template <class S>
inline int SafeConvert<int>( S value ) {

    ASSERT( value >= S(INT_MIN) && value <= S(INT_MAX) );
    return int(value);
} /// error C2768: 'SafeConvert' : illegal use of explicit template arguments


template <class S>
inline size_t SafeConvert<size_t>( S value ) {

    ASSERT( value >= S(0) && value <= S(size_t(-1)) );
    return size_t(value);
} /// error C2768: 'SafeConvert' : illegal use of explicit template arguments


// ...

void test() {

    size_t v = INT_MAX+1;
    int iv = SafeConvert<int>(v);
}

However I have the following come compilation errors:

error C2768: 'SafeConvert' : illegal use of explicit template arguments

My question is how to tell the compiler that I want to specialize only the D class ?

Thanks.

Answer 1

You can’t partially specialize function templates. You need to mimic it with a class wrapper or use standard function overloading. An example of mimicing:

template <typename T1, typename T2>
struct processor;

template < typename T1, typename T2 >
T1 fun(T2 t2) { return processor<T1,T2>::apply(t2); }

template < typename T2 >
struct processor<int,T2>
{
   static int apply(T2 t2) { .... }
};

...etc...