Chapter 35: Dynamic type

Section 35.1: Creating a dynamic object with properties

using System;

using System.Dynamic;

dynamic info = new ExpandoObject(); info.Id = 123;

info.Another = 456;

Console.WriteLine(info.Another);

// 456

Console.WriteLine(info.DoesntExist);

// Throws RuntimeBinderException

Section 35.2: Creating a dynamic variable

dynamic foo = 123; Console.WriteLine(foo + 234);

// 357 Console.WriteLine(foo.ToUpper())

// RuntimeBinderException, since int doesn't have a ToUpper method

foo = "123"; Console.WriteLine(foo + 234);

// 123234

Console.WriteLine(foo.ToUpper()):

// NOW A STRING

Section 35.3: Returning dynamic

using System;

public static void Main()

{

var value = GetValue(); Console.WriteLine(value);

// dynamics are useful!

}

private static dynamic GetValue()

{

return "dynamics are useful!";

}

Section 35.4: Handling Specific Types Unknown at Compile

Time

The following output equivalent results:

class IfElseExample

{

public string DebugToString(object a)

{

if (a is StringBuilder)

{

return DebugToStringInternal(a as StringBuilder);

}

else if (a is List<string>)

{

return DebugToStringInternal(a as List<string>);

}

else

{

return a.ToString();

}

}

private string DebugToStringInternal(object a)

{

// Fall Back

return a.ToString();

}

private string DebugToStringInternal(StringBuilder sb)

{

return $"StringBuilder - Capacity: {sb.Capacity}, MaxCapacity: {sb.MaxCapacity}, Value: {sb.ToString()}";

}

private string DebugToStringInternal(List<string> list)

{

return $"List<string> - Count: {list.Count}, Value: {Environment.NewLine + "\t" + string.Join(Environment.NewLine + "\t", list.ToArray())}";

}

}

class DynamicExample

{

public string DebugToString(object a)

{

return DebugToStringInternal((dynamic)a);

}

private string DebugToStringInternal(object a)

{

// Fall Back

return a.ToString();

}

private string DebugToStringInternal(StringBuilder sb)

{

return $"StringBuilder - Capacity: {sb.Capacity}, MaxCapacity: {sb.MaxCapacity}, Value: {sb.ToString()}";

}

private string DebugToStringInternal(List<string> list)

{

return $"List<string> - Count: {list.Count}, Value: {Environment.NewLine + "\t" + string.Join(Environment.NewLine + "\t", list.ToArray())}";

}

}

The advantage to the dynamic, is adding a new Type to handle just requires adding an overload of DebugToStringInternal of the new type. Also eliminates the need to manually cast it to the type as well.