Getting value from anonymous type? [duplicate]

Answer 1

Note that returning anonymous types or Tuple<> from a method is a bad thing to do

But you asked a question about how to do it, not about "is it a good idea"...

By using dynamic or reflection...

dynamic b = Test();
string str = b.A;

Or by cheating:

public static object Test()
{
    return new { A = "Test" };
}

public static string GetA(object obj)
{
    // We create an anonymous type of the same type of the one in Test()
    // just to have its type.
    var x = new { A = string.Empty };

    // We pass it to Cast, that will take its T from the type of x
    // and that will return obj casted to the type of the anonymous
    // type
    x = Cast(x, obj);

    // Now in x we have obj, but strongly typed. So x.A is the value we
    // want
    return x.A;
}

public static T Cast(T type, object obj) where T : class
{
    return (T)obj;
}

string str = GetA(Test());

In C# all the anonymous types with the same properties of the same type that are in the same assembly are merged together. So the new { A } of Test() and of GetA() are of the same type.

The Cast is a useful trick to extract the type from an anonymous type. You pass as the first parameter your typed anonymous type (the parameter is used only to "activate" the generic T) and as the second parameter the object you want to cast. Similar tricks can be used to create collections of generic types, like

public static T MakeList(T type)
{
    return new List();
}