Making a generic type for Tuples

Question

I've clearly established how to make a generic Tuple as follows when the number of items is known in advance...

        Type t = typeof(Tuple<,,>);
        Type[] keys = new Type[] { typeof(string), typeof(string), typeof(int) };
        Type specific = t.MakeGenericType(keys);

but what if the number of objects in the "keys" array is variable? How to you start the ball rolling with the initial assignment to "t"?

Cheers. Craig

Answer 1

Personally, I would have an array of the generic type definitions:

Type[] tupleTypes = {
    typeof(Tuple<>),
    typeof(Tuple<,>),
    typeof(Tuple<,,>),
    typeof(Tuple<,,,>),
    typeof(Tuple<,,,,>),
    typeof(Tuple<,,,,,>),
    typeof(Tuple<,,,,,,>),
    typeof(Tuple<,,,,,,,>),
};

You could do this in code, but it would be a bit of a pain... probably something like:

Type[] tupleTypes = Enumerable.Range(1, 8)
                              .Select(x => Type.GetType("System.Tuple`" + x)
                              .ToArray();

Or avoiding the array:

Type generic = Type.GetType("System.Tuple`" + keys.Length);
Type specific = generic.MakeGenericType(keys);

Answer 2

Yet another way of building tupleTypes through Tuple.Create:

// once
Type[] tupleTypes = typeof(Tuple).GetMethods(BindingFlags.Public | BindingFlags.Static)
    .Where(mi => mi.IsGenericMethod && mi.Name == "Create")
    .Select(mi => mi.ReturnType.GetGenericTypeDefinition())
    .Distinct() // make sure there is no duplicated return types
    .OrderBy(t => t.GetGenericArguments().Length)
    .ToArray(); // expect start from Tuple<>

// instant type creation
Type tupleType = tupleTypes[types.Length-1].MakeGenericType(types);

Of course that expects that class System.Tuple will contain static Create methods that only produces Tuple<...>.