Compare without generics

Question

I have a bit complicated issue to solve.

I have a list of objects though later the list will be filled with two different type of instances.

First type is MyFirstType<T1, T2> and second type is MySecondType<T>

Now I need to run though the list of objects and ask which one of the two is each item. Then I need to do some custom logic on the item.

For example:

foreach(object obj in list)
{
   if(obj is MyFirstType<T1, T2>)
   {
     // do something
   }
   else if(obj is MySecondType<...>)
   {
   }
}

The problem is T or T1 and T2 could be any types so how do I write such an if - Is Keyword statement that only comparies if MyFirstType but not the generics inside? if(obj is MyFirstType<T1, T2>) does not work since it needs concrete types for T1 and T2.

Like mentioned just need comparison without T1 and T2. Any ideas how to solve this?

This kind of type checking is almost always a product of taking the wrong approach to solve a problem; can you be a bit less abstract and detail what the actual task is and how you're trying to solve it? — Ant P, Apr 21 '14 at 19:44
@AntP Thanks but no thanks The question was not shall I change my design or not. It is clear enough what the problem is. If you cannot solve this please do not start discussion how could/should it have been done right. — dev hedgehog, Apr 21 '14 at 19:47
@devhedgehog That is a pretty poor attitude but, sure, have it your way. I'm not going to waste my time helping you implement a sub-par solution, though I'm sure others will. — Ant P, Apr 21 '14 at 19:48

score 2 · Accepted Answer · answered Apr 21 '14 at 19:44

You can use IsGenericType property of Type class to check if obj.GetType() is generic, and then use GetGenericTypeDefinition to get generic type definition, which can be compared to typeof(MyFirstType<,>) and typeof(MySecondType<>):

foreach(object obj in list)
{
    if(obj.GetType().IsGenericType)
    {
        if(obj.GetType().GetGenericTypeDefinition() == typeof(MyFirstType<,>))
        {
          // do something
        }
        else if(obj.GetGenericTypeDefinition() == typeof(MySecondType<>))
        {
        }
    }
}

score 2 · Answer 2 · answered Apr 21 '14 at 19:44

2

The cheap solution: create a flag interface which you derive in your types. This is just a helper to determine the type.
Use reflection and check the type definition and check the name of the type.

answered Apr 21 '14 at 19:44

Patrick Hofman

153,850
22
249
325

score 2 · Answer 3 · answered Apr 21 '14 at 20:02

2

Why don't you use polymorphism? Have the two types implement an interface with a common method. Then in the implementation of each type write the code for the method you need.

public interface ICommon
{
    void DoThis();
}

For MyFirstType and MySecondType you will have:

public class MyFirstType<T> : ICommon
{
    public void DoThis()
    {
        //DoThis
    }
}

public class MySecondType<T1,T2> : ICommon
{
    public void DoThis()
    {
        //DoThis
    }
}

Then you could write the following foreach loop:

foreach(object obj in list)
{
    obj.DoThis();
}

answered Apr 21 '14 at 20:02

Ben

538
1
9
24

1

+1 for a good answer, though likely a wasted effort given comments. – Ant P Apr 21 '14 at 20:03
I cannot change the types. They are third party. They are sealed. Thanks Ben anyway. I appreciate your suggestion. @AntP This is not a waisted efford however your comments are waisted efford. Havent you said you moved on? – dev hedgehog Apr 21 '14 at 21:08

Compare without generics

3 Answers3