Delegates, Anonymous Methods & Lamda Expressions

Jasminder Singh
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This article explains the basic concept of delegates, anonymous methods and lamda expressions. We will use one single code example of an add method that takes two input parameters and returns their sum. So we have a simple function with the code as:

public static Int32 Add(Int32 a, Int32 b)
{
return a + b;
}

Delegate

You might have seen the same definition on the other sources. A delegate acts as a function pointer and can be used to execute a function, by simply passing its name (to register that method) and then invoke it, by calling the delegate instance. But the condition is that the signature of the delegate must be the same as that of the function that we need to call through this delegate.

So now we will use a delegate to call the preceding method. For this, we need to first create a delegate as in the following:

public delegate Int32 Calculate(Int32 a, Int32 b);
Calculate _calculate = new Calculate(Add);
Console.Write("Sum of numbers using Delegate : " + _calculate(21, 22));

Anonymous methods

Anonymous methods were introduced in C# 2.0, as a shorter syntax for passing the function definition directly to the delegate parameter, instead of creating a method and passing its name explicitly to it. We can simply pass the logic of our function inside the delegate call, instead of creating a function for it.

So now we will convert the code above to calculate the sum using an anonymous method.

Calculate _calculate = delegate(Int32 a, Int32 b)
{
return a + b;
};
Console.Write("Sum of numbers using Anonymous method : " + _calculate(50, 50));

As we can see above, we replaced the original function name with the actual function logic, in the delegate initialization. Run the code and see the results.

Lamda expressions

Finally we have the concept of lamda expressions. Introduced in C# 3.5, they further shorten the syntax of creating anonymous methods. It uses the => or lamda operator, to declare the anonymous methods. Let's convert our code to use the lamda expression.

Calculate _calculate2 = (a, b) => a + b;
Console.Write("Sum of numbers using Lamda expressions : " + _calculate2(10, 10));

To specify any input parameters, we set them on the left of the => operator, in the brackets, as we did above (a, b). If we do not have any input parameter, we can simply use empty brackets as (). On the other hand, the statements on the right side of the => operator are called a lamda expression. If we need to have multiple statements in the lamda expression, we need to use the {} brackets to enclose them and then they are called a lamda statement (Source: MSDN).

The procedure to call the delegate remains the same. What changes is how we use the actual function with the delegate created for it. The complete code is listed below:

create delegate

Lamda expressions in LINQ query

lamda expressions are used extensively in the linq queries. You must have written the queries like below:

List<Int32> _lst = new List<Int32>();
_lst.Where(x => x > 10).ToList();

Let's try to see why we can use the lamda expressions here. See the code below:

As we can see, it expects a Func<int, bool> delegate, that takes an input parameter and returns a boolean value. Since we can directly provide a lamda expression based definition to the delegate, like we did above in our Calculate example, we can directly write the lamda expressions with these methods. In fact we can write the anonymous method directly in this method or could have declared the Func delegate explicitly, with anonymous method syntax and then pass it to this method. So we can have the code as: