Question

I meet a problem about type contraint of c# now.

I wrote a pair of methods that can convert object to string and convert string to object.
ex.

static string ConvertToString(Type type, object val) {
 if (type == typeof(string)) return (string)val;
 if (type == typeof(int)) return val.ToString();
 if (type.IsSubclassOf(typeof(CodeObject))) return ((CodeObject)val).Code;
}

static T ConvertToObject<T>(string val) {
 Type type = typeof(T);
 if (type == typeof(string)) return (T)(object)val;
 if (type == typeof(int)) return (T)(object)int.Parse(val);
 if (type.IsSubclassOf(typeof(CodeObject))) return Codes.Get<T>(val);
}

where CodeObject is a base class of Employees, Offices …,
which can fetch by static method Codes.Get where T: CodeObject

but the code above cannot be compiled because error #CS0314

the generic type T of method ConvertToObject have no any constraint
but Codes.Get request T must be subclass of CodeObject

i tried use overloading to solve the problem but not ok.

is there any way to clear up the problem? like reflection?

Answer 1

i tried to clear up the problem by reflection.

if (type.IsSubclassOf(typeof(CodeObject))) {
    var baseMethod = typeof(Codes).GetMethod("Fetch<>", BindingFlags.Static | BidingFlags.Public, null, new Type[] {typeof(string)}, null);
    if (baseMethod != null) {
        var genericMethod = baseMethod.MakeGenericMethod(type);
        if (genericMethod != null)
            return (T)genericMethod.Invoke(null, new string[] { val });
    }
}