Some help Generics

[Rauland]

Hi,

Lets say I have a function,which accepts as a parameter a string.

Depending on the value of this string I would like to return a generic list of different types.

So, for instance:

Lets say I pass in the word,"dogs", well then I´d like to return List<Dogs> mydogList = new List<Dogs>();

If I pass in the word "cars", well the same thing,return List<Cars> myCarlist = new List<Cars>();

My function I had in mind would be something similiar to:
(Please note that the code below is incorrect!)

Public List<T> MyFunction(String str)
{
switch (str)
case "Dogs":
return  List<dogs> dogsList = new list<dogs>();
Case "Cars":
return List<cars> carList = new list<cars>();
}

But this obviously doesn´t work,...

Could sb please shine some light on how to improve my approach, or take a totally different one?
Thanks !

[jmcilhinney]

You cannot do what you want by passing a string. You could do it by passing an instance of the type you wanted to make the list items, e.g.

private void Form1_Load(object sender, EventArgs e)
{
    List<int> integers = this.CreateList(0);
 
    List<string> strings = this.CreateList("");
}
 
public List<T> CreateList<T>(T type)
{
    return new List<T>();
}

If you do it the way you are currently you would have to add a case for every type you wanted to support. In that case your cases should look like this:

case "String"
    return new List<string>();

[Rauland]

Hi Thanks,

I eventualy opted for an easier approach sth like:

List<dog> dogs;
List<car> cars;

private void LoadList(string str)
{
switch(str)
{
case dog:
            dogs = new List<dog>();
            dogs.add(new dog("jimmy"));
            break;
case car:
            cars = new List<car>()
            ,....
            ,..
}
}
}

It would be great though to somehow combine your code with this approach;

Sth like:

Private List<T> LoadList<T>(T type)
{
Problem (1)
switch(type.GetType())
{
case dog.GetType():
      List<T> dogList = new List<T>();
      problem(2)("Would like to add dog items")
      return dogList;


case car.GetType():
break;
}

But, run into problems.
1) First I find I can´t do a Switch based on a variable´s type.
2) I can only return an empty List<T>. So if the type is "Car", I will only be able to return an empty,List<Car>, I mean by empty, with no Car items.
I can´t add Car items to the list from within the switch, as I would need Car objects, and I can´t add them to a List<T> type.

Maybe I am over complicating things, but just would like to learn how to do things in a different way,..
Thanks!

[jmcilhinney]

You're trying to do things in a way that they were never intended. You would have to look into reflection.