Passing variable type to recursive factory as generic

Question

I am trying to write my own factory method for educational purposes when I bumped into the following issue; when trying to call my function recursively, I cant pass a specified type to the generic receptor.

Note: this may have nothing to do with the design pattern at all, this may just be something basic I am doing wrong. Either way, I am a bit stumped.

public static T SpawnObject<T>()
{ 
    var objType = typeof(T);
    var parameters = objType.GetConstructors().Single().GetParameters();
    List<object> paramObjects;

    if (!parameters.Any()) return (T)Activator.CreateInstance(objType);

    paramObjects = new List<object>();
    foreach (var item in parameters)
    {
        //var arg = Activator.CreateInstance(item.ParameterType);
        var paramType = item.ParameterType;
        var arg = SpawnObject<paramType>(); // UNABLE TO ID 'PARAMTYPE' ??
        paramObjects.Add(arg);
    }

    T returnInstance = (T)Activator.CreateInstance(objType, paramObjects.ToArray());
    return returnInstance;
}

Thanks in advance to anyone that can help me understand why this is failing.

possible duplicate of [Generics in C#, using type of a variable as parameter](http://stackoverflow.com/questions/2107845/generics-in-c-using-type-of-a-variable-as-parameter) — dtb, Mar 29 '14 at 00:18

score 2 · Accepted Answer · answered Mar 29 '14 at 00:23

See the question I linked above why you can't use a variable as type parameter.

Here's a simple solution:

public static T SpawnObject<T>()
{
    return (T)SpawnObject(typeof(T));
}

private static object SpawnObject(Type objType)
{
    var parameters = objType.GetConstructors().Single().GetParameters();
    List<object> paramObjects;

    if (!parameters.Any()) return Activator.CreateInstance(objType);

    paramObjects = new List<object>();
    foreach (var item in parameters)
    {
        //var arg = Activator.CreateInstance(item.ParameterType);
        var paramType = item.ParameterType;
        var arg = SpawnObject(paramType);
        paramObjects.Add(arg);
    }

    return Activator.CreateInstance(objType, paramObjects.ToArray());
}

Great thanks - I obviously didn't look hard enough for an answer initially. — DawnFreeze, Mar 29 '14 at 00:26

Passing variable type to recursive factory as generic

1 Answers1