A Basic Tour To Dynamic Keyword - Dotnet 4.0

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Introduction

With the advent of C#4.0, we have a new friend… Dynamic.

It references objects which happens to or not to exist at runtime. Put in different term, it allows late binding.

Using the code

Let us start with a very basic example

Example 1: Simple Addition

dynamic dynVar = 10;
dynVar += 10;
Console.WriteLine(dynVar);

Output is: 20

Example 2: Simple Concatenation

dynVar += " Hello";
Console.WriteLine(dynVar);

Output is: 10 Hello

But consider this

var varVariable = 10;
varVariable += " Hello";

This will yield a compile time error

Cannot implicitly convert type 'string' to 'int'

However the below works

object obj = 10;
obj += "Hello";
Console.WriteLine(obj);

Reason: It is a specific type inferred from context and does not change type like dynamic does

Example 3:

Consider the below

dynamic dynClass = new MyClass()
{
  IntProperty = 1
                    
  , StringProperty = "A string property"
                    ,
  , StringField = "A string filed"
                    ,
  , DecimalField = 10d
};

And

var varClass = new MyClass()
{
   IntProperty = 1
                    ,
   StringProperty = "A string property"
                    ,
   StringField = "A string filed"
                    ,
   DecimalField = 10d
};

TestCase1 : Display Valid Property value

Console.WriteLine(dynClass.IntProperty); //Using dynamic object
Console.WriteLine(varClass.IntProperty); //using var object

Worked with a charm with the output being 1 for each case.

TestCase2 : Display InValid Property value

Console.WriteLine(dynClass.InvalidProperty); //Using dynamic object

Compiled fine

Runtime Error: 'DynamicExample.MyClass' does not contain a definition for 'InvalidProperty'

 Console.WriteLine(varClass.InvalidProperty); //using var object
 

Complie time error DynamicExample.MyClass' does not contain a definition for 'InvalidProperty' and no extension method 'InvalidProperty' accepting a first argument of type 'DynamicExample.MyClass' could be found (are you missing a using directive or an assembly reference?)

TestCase3 : Display Valid Function Call

Console.WriteLine(dynClass.ValidMethod()); //Using dynamic object
Console.WriteLine(varClass.ValidMethod()); //using var object

As expected, worked fine with the output being Hello

TestCase4 : Display InValid Function Call

Console.WriteLine(dynClass.InvalidMethod()); //Using dynamic object

Runtime error 'DynamicExample.MyClass' does not contain a definition for 'InvalidMethod'

Console.WriteLine(varClass.InvalidMethod()); //using var object

Compile time error as expected 'DynamicExample.MyClass' does not contain a definition for 'InvalidMethod' and no extension method 'InvalidMethod' accepting a first argument of type 'DynamicExample.MyClass' could be found (are you missing a using directive or an assembly reference?)

Example 4: Runtime invocation

Consider the below two cases

Case 1

//Case 1: Using reflection to invoke member
var type = typeof(DynamicExample.MyClass);
var res1 = type.InvokeMember(
            "Add"
            , BindingFlags.InvokeMethod
            , null
            , Activator.CreateInstance(type)
            , new object[] { 10, 20 });
Console.WriteLine("Addition of two number using reflection= " + res1);

Case 2

//Case 2: Using Dynamic to invoke member 
 dynamic res2 = ((dynamic)Activator.CreateInstance(typeof(DynamicExample.MyClass))).Add(10, 20);
 Console.WriteLine("Addition of two number using dynamic= " + res2);

The output being same in both the cases.

Example 5: Calling Iron Python Function From C# 4.0

Here I will give a short demo as how to call a method written in IronPython 2.6 and making a dynamic invocation to the method from C# environment.

Step 1: Download the latest version of Iron Python from Code Plex

Step 2: Install the software.

Step 3: For this demo I am using “first.py” python file located inside the Tutorial Folder

The file has two methods

a) Add

b) Factorial.

For this demo purpose, let us only invoke the Add method that performs addition of two numbers being supplied as parameters to the method.

Step 4: I am using a console application for the demo purpose. The very first thing we need to do is to add the dlls as shown under

Step 5: The function invocation happens in just three steps as shown below

static void Main(string[] args)
        {
            //Step 1: 
            //Creating a new script runtime             
            var ironPythonRuntime = Python.CreateRuntime();

            try
            {
                //Step 2:
                //Load the Iron Python file/script into the memory
                //Should be resolve at runtime
                dynamic loadIPython = ironPythonRuntime.UseFile("first.py");

                //Step 3:
                //Invoke the method and print the result
                Console.WriteLine(
                string.Format("Addition result from IronPython method for {0} 
                 and {1} is {2}",100,200, loadIPython.add(100, 200)));
            }
            catch (FileNotFoundException ex)
            {
                Console.WriteLine(ex.Message);
            }
            Console.ReadKey(true);
            
        }

The very first line

var ironPythonRuntime = Python.CreateRuntime();

loads the Iron Python libraries along with the DLR code needed to execute the python script.

Second line

dynamic loadIPython = ironPythonRuntime.UseFile("first.py");

loads the python script into memory. The significance of the dynamic variable(loadIPython) here is being the fact that Python calls are resolve at runtime.

The last line i.e.

     Console.WriteLine(string.Format("
          Addition result from IronPython method for {0} and {1} 
          is {2}", 100,200, 
          loadIPython.add(100, 200)) );

Is simply to invoke the Python method and to display the result.

Step 6: And here is the output

Example 6: Calling Iron Ruby Function From C# 4.0

Here I will give a short demo as how to call a method written in IronRuby 1.1 and making a dynamic invocation to the method from C# environment.

Step 1: Download the latest version of Iron Ruby from Code Plex

Step 2: Install the software.

Step 3: For this demo I am using add.rb Ruby file which has only one Add method that performs addition of two numbers being supplied as parameters to the method.

Step 4: I am using a console application for the demo purpose. The very first thing we need to do is to add the dlls as show below

Step 5: The function invocation happens in just three steps as shown below

static void Main(string[] args)
        {
            //Step 1: 
            //Creating a new script runtime   
            var ironRubyRuntime = Ruby.CreateRuntime();

            try
            {
                //Step 2:
                //Load the Ruby file/script into the memory
                //Should be resolve at runtime
                dynamic loadIRuby = ironRubyRuntime.UseFile(@"add.rb");

                //Step 3:
                //Invoke the method and print the result
                Console.WriteLine(
                string.Format("Addition result from Iron Ruby method for {0} and 
                {1} is {2}",100, 200, loadIRuby.add(100, 200))
                                 );               
            }
            catch (FileNotFoundException ex)
            {
                Console.WriteLine(ex.Message);
            }
            Console.ReadKey(true);
        }

The very first line

var ironRubyRuntime = Ruby.CreateRuntime();

loads the Iron Ruby libraries along with the DLR code needed to execute the python script.

Second line

dynamic loadIRuby = ironRubyRuntime.UseFile(@"add.rb");

loads the Ruby script into memory. The significance of the dynamic variable(loadIRuby) here is being the fact that Ruby calls are resolve at runtime.

The last line i.e.

Console.WriteLine(string.Format
("Addition result from Iron Ruby method for {0} 
and {1} is {2}", 100, 200, 
loadIRuby.add(100, 200)));

Is simply to invoke the Ruby method and to display the result.

Step 6: And here is the output

References

http://msdn.microsoft.com/en-us/library/dd264736.aspx

Conclusion:

In this short tutorial we have seen how the dynamic keyword helps us in various situations. Having said that, there are some pitfalls of this keyword like runtime checking and henceforth breaks the hallmark of C#’s strong type checking. Hope this tutorial has shed some idea on how, where to use dynamic and also how to invoke IronPython and IronRuby methods from C# 4.0.

Comments on the topic are highly appreciated for the improvement of the topic.

Thanks for reading the article.