C#•2y ago

✅ Switching on a type object

Is there a way to do a switch on a type object? I've got a function that takes a type and returns an enum value for specific types. Currently I've had to do it like this:

private static MyValueType GetValueTypeFromType(Type value)
{
    if(value == typeof(string))
    {
        return MyValueType.String;
    }

    if(value == typeof(bool))
    {
        return MyValueType.Bool;
    }

    if(value == typeof(int))
    {
        return MyValueType.Int;
    }

    return MyValueType.Invalid;
}

private static MyValueType GetValueTypeFromType(Type value)
{
    if(value == typeof(string))
    {
        return MyValueType.String;
    }

    if(value == typeof(bool))
    {
        return MyValueType.Bool;
    }

    if(value == typeof(int))
    {
        return MyValueType.Int;
    }

    return MyValueType.Invalid;
}

However, I'd like to be able to make this code more concise. I could do it with a Dictionary, but if there's a better way of doing this, I'd love to hear it:

Dictionary<Type, MyValueType> valueTypes = new()
{
    [typeof(string)] = MyValueType.String,
    [typeof(bool)] = MyValueType.Bool,
    [typeof(int)] = MyValueType.Int,
};

Dictionary<Type, MyValueType> valueTypes = new()
{
    [typeof(string)] = MyValueType.String,
    [typeof(bool)] = MyValueType.Bool,
    [typeof(int)] = MyValueType.Int,
};

5 Replies

HimmDawg•2y ago

You can only use pattern matching in a switch statement, if you have an object, not the type object itself. So you have to rely on a dictionary, or maybe even switch on the name of the type.

HughOP•2y ago

Okay - thanks - that's good to know I'm happy with the dictionary approach. I made the actual dictionary a private static readonly field, so it isn't re-generating each time

HimmDawg•2y ago

I think there is some syntax like

switch (type)
{
  case Type t1 when t1 == typeof(int): ...
}

switch (type)
{
  case Type t1 when t1 == typeof(int): ...
}

but it's not really better than if/else 😄

ero•2y ago

in fact i'm pretty sure it's a lot worse the compiler can optimize if (typeof(T) == typeof(int)) ...

HughOP•2y ago

Thanks - I think I'll stick with the ifs then

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✅ Switching on a type object