在通用方法中使用类型为Class的switch

Question

Is it possible to use the switch when comparing Classes in a generic method? Example:

switch (typeof(T))
{
    case typeof(Class1):
        // ...
        break;

    case typeof(Class2):
        // ...
        break;

    default:
        break;
}

The idea is not to use the name but the Class object. At moment I'm using:

if (typeof(T) == typeof(Class1))
{
   // ...
}
else if (typeof(T) == typeof(Class2))
{
   // ...
}

For simplicity, it would be good to use the switch.

Answer 1

In cases like this, I use dictionaries, paired with values of lambdas as fit for the specific problem at hand.

var options = new Dictionary<Type, Action>()
{
    { typeof(string), () => doSomething() },
    { typeof(int), () => doSomething() },
    ...
};

Action act = null;
if (options.TryGetValue(typeof(T), out act) {
    act();
} else {
   // default
}

The dictionary is usually a static readonly field or property, so the indexing is done just once.

In your specific case you can get along with a Dictionary<Type, Func<object, string>> , like so:

private static readonly Formatters = new Dictionary<Type, Func<object, string>>()
{
    { typeof(Class1), o => ((Class1)o).format() },
    { typeof(Class2), o => FormatClass.FormatClass2((Class2)o) },
    ...
};

T instance;
string formatted = Formatters[typeof(T)](instance);

Answer 2

If you are using C# 7, you can make use of pattern matching.

For example,

public void Method<T>(T param)
{
    switch(param)
    {
        case var _ when param is A:
        Console.WriteLine("A");
        break;
        case var _ when param is B:
        Console.WriteLine("B");
        break;

    }
}

Where

public class A{}
public class B{}

Answer 3

Expanding on Anu Viswan 's answer , Since C# 7.1, this is valid:

public void Method<T>(T param)
{
    switch (param)
    {
        case A a:
            Console.WriteLine("A");
            break;
        case B b:
            Console.WriteLine("B");
            break;
    }
}