Simple Func delegate example with LINQ in .NET C#

Say you’d like to filter an array of integers:

int[] ints = new int[] { 1, 2, 3, 4, 5, 6, 7, 8 };

You’re only interested in integers greater than 3. There are many ways to filter an array of T. One of them is using a Func delegate. Func delegates come in the following forms:

public delegate TR Func<TR>();
public delegate TR Func<Arg0, TR>(Arg0 a0);
public delegate TR Func<Arg0, Arg1, TR>(Arg0 a0, Arg1 a1);
.
.
.
public delegate TR Func<Arg0, Arg1, Arg2, Arg3, TR>(Arg0 a0, Arg1 a1, Arg2 a2, Arg3 a3);

…where TR is the return type of function and Arg(x) is the input parameter type. Note that the return type is the last element of the parameter types.

One of the overloaded versions of the LINQ Where operator accepts a Func delegate:

IEnumerable<T> Where<T>(this IEnumerable<T> source, Func<int, bool> predicate);

So we declare our Func:

Func<int, bool> GreaterThanTwo = i => i > 3;

Then we declare our query:

IEnumerable<int> intsGreaterThanTwo = ints.Where(GreaterThanTwo);

We finally enumerate the query:

foreach (int i in intsGreaterThanTwo)
{
        Console.WriteLine(i);
}

You can view all LINQ-related posts on this blog here.