How to find the minimum covariant type for best fit between two types?

Question

There\'s IsAssignableFrom method returns a boolean value indicates if one type is assignable from another type.

How can we not only test if they are as

Answer 1

The simplest case would be iterating over the base types of one object and checking them for being assignable with the other type, like this:

• Code

  public Type GetClosestType(Type a, Type b) {
      var t=a;
  
      while(a!=null) {
          if(a.IsAssignableFrom(b))
              return a;
  
          a=a.BaseType;
      }
  
      return null;
  }
  

This will produce System.Object for two types which are unrelated, if they are both classes. I'm not sure if this behaviour met your requirement.

For more advanced cases, I'm using a custom extension method called IsExtendablyAssignableFrom.

It can handle different numeric types, generics, interfaces, generic parameters, implicit conversions, nullable, boxing/unboxing, and pretty much all the types I have come across with when implementing my own compiler.

I've uploaded the code into a separate github repository [here], so you could use it in your project.