Is there a better alternative than this to 'switch on type'?

Question

Seeing as C# can\'t switch on a Type (which I gather wasn\'t added as a special case because is relationships mean that more than one distinct

Answer 1

Create an interface IFooable, then make your A and B classes to implement a common method, which in turn calls the corresponding method you want:

interface IFooable
{
    public void Foo();
}

class A : IFooable
{
    //other methods ...

    public void Foo()
    {
        this.Hop();
    }
}

class B : IFooable
{
    //other methods ...

    public void Foo()
    {
        this.Skip();
    }
}

class ProcessingClass
{
    public void Foo(object o)
    {
        if (o == null)
            throw new NullRefferenceException("Null reference", "o");

        IFooable f = o as IFooable;
        if (f != null)
        {
            f.Foo();
        }
        else
        {
            throw new ArgumentException("Unexpected type: " + o.GetType());
        }
    }
}

Note, that it's better to use as instead first checking with is and then casting, as that way you make 2 casts, so it's more expensive.

Answer 2

Should work with

case type _:

like:

int i = 1;
bool b = true;
double d = 1.1;
object o = i; // whatever you want

switch (o)
{
    case int _:
        Answer.Content = "You got the int";
        break;
    case double _:
        Answer.Content = "You got the double";
        break;
    case bool _:
        Answer.Content = "You got the bool";
        break;
}

Answer 3

Given inheritance facilitates an object to be recognized as more than one type, I think a switch could lead to bad ambiguity. For example:

Case 1

{
  string s = "a";
  if (s is string) Print("Foo");
  else if (s is object) Print("Bar");
}

Case 2

{
  string s = "a";
  if (s is object) Print("Foo");
  else if (s is string) Print("Bar");
}

Because s is a string and an object. I think when you write a switch(foo) you expect foo to match one and only one of the case statements. With a switch on types, the order in which you write your case statements could possibly change the result of the whole switch statement. I think that would be wrong.

You could think of a compiler-check on the types of a "typeswitch" statement, checking that the enumerated types do not inherit from each other. That doesn't exist though.

foo is T is not the same as foo.GetType() == typeof(T)!!

Answer 4

As Pablo suggests, interface approach is almost always the right thing to do to handle this. To really utilize switch, another alternative is to have a custom enum denoting your type in your classes.

enum ObjectType { A, B, Default }

interface IIdentifiable
{
    ObjectType Type { get; };
}
class A : IIdentifiable
{
    public ObjectType Type { get { return ObjectType.A; } }
}

class B : IIdentifiable
{
    public ObjectType Type { get { return ObjectType.B; } }
}

void Foo(IIdentifiable o)
{
    switch (o.Type)
    {
        case ObjectType.A:
        case ObjectType.B:
        //......
    }
}

This is kind of implemented in BCL too. One example is MemberInfo.MemberTypes, another is GetTypeCode for primitive types, like:

void Foo(object o)
{
    switch (Type.GetTypeCode(o.GetType())) // for IConvertible, just o.GetTypeCode()
    {
        case TypeCode.Int16:
        case TypeCode.Int32:
        //etc ......
    }
}

Answer 5

I use

    public T Store<T>()
    {
        Type t = typeof(T);

        if (t == typeof(CategoryDataStore))
            return (T)DependencyService.Get<IDataStore<ItemCategory>>();
        else
            return default(T);
    }

Answer 6

You can create overloaded methods:

void Foo(A a) 
{ 
    a.Hop(); 
}

void Foo(B b) 
{ 
    b.Skip(); 
}

void Foo(object o) 
{ 
    throw new ArgumentException("Unexpected type: " + o.GetType()); 
}

And cast the argument to dynamic type in order to bypass static type checking:

Foo((dynamic)something);