Dynamic keyword in C#

Tuba Mansoor

5 years ago

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She works with an IT major. Normally she doesn't speak much but when she speaks, I bet she can make you speechless. Total nerd and travel buff Tuba can be seen passionately doing gyms, Netflix or sharing experiences through excellent blogs. If not then you can find her learning something new. Yes, She knows 4 languages – English, Hindi, Marathi, and German.

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There are two kinds of languages – Static(C#, Java) and Dynamic (Ruby, Javascript & Python).

In static the types are checked before execution, and in dynamic it is checked after execution.

C# is primarily a static language, but in .NET 4 dynamic features were introduced to provide more flexibility for things that earlier used reflection. DLR (Dynamic Language Runtime) was added to deal with this.

 class Program
    {
        static void Main(string[] args)
        {
            dynamic d = "test";
            d = 10;
            Console.WriteLine("Hello World!");
        }
    }

Look at the above piece of code. We can write the above code and C# will not throw an error. If we debug the code, we will find that the type of d is earlier set as a string which is later changed to int.

But let’s do something like this.

class Program
    {
        static void Main(string[] args)
        {
            dynamic d = "test";
            d++;
            //d = 10;
            //Console.WriteLine("Hello World!");
        }
    }

This will not throw a compile-time error, but it will throw a runtime error.

Difference between var and dynamic?

var is used when you don’t want to define a type and let the compiler decide it for you. For example in the following piece of code, var will be defined as a string during compile time itself.

var x = "this is string";

What about cases in which both dynamic and var are mixed like in the below example?

 class Program
    {
        static void Main(string[] args)
        {
            dynamic d1 = 10;
            dynamic d2 = 5;
            var v = d1 + d2;

        }
    }

In the above case, d1,d2 and v will be defined as dynamic during compile time and dynamic(int) during runtime.

Another advantage of using the dynamic keyword is that we don’t have to explicitly used ‘ConvertToInt32’ or ‘Convert.ToString()’ etc. When we assign a value to the dynamic, the conversion will happen automatically.

That’s all about using the dynamic keyword in C#!

Difference between var and dynamic?

Further Reading

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