Posted by: Cirilo Meggiolaro | 02/2/2009

Tip of the day #111 – Func delegate

Tip #110 explored the Action delegate that may be used to encapsulate a delegate method that does not accept parameters and does not have a return value. Today we are going to check the Func<TResult> delegate and its overloads to have more flexibility on using delegates with methods that return value and / or accept parameters.

Overloads

The following overloads are available:

  • It does not accept parameters but returns a value;

public delegate TResult Func<TResult>();

  • It accepts one parameter and returns a value;

public delegate TResult Func<T, TResult>(T arg);

  • It accepts two parameters and returns a value;

public delegate TResult Func<T1, T2, TResult>(T1 arg1, T2 arg2);

  • It accepts three parameters and returns a value;

public delegate TResult Func<T1, T2, T3, TResult>(T1 arg1, T2 arg2, T3 arg3);

  • It accepts four parameters and returns a value.

public delegate TResult Func<T1, T2, T3, T4, TResult>(T1 arg1, T2 arg2, T3 arg3, T4 arg4);

How to…

The following example shows a call to a method that retrieves a Boolean value:

private bool M()
{
    return false;
}

[…]

Func<bool> myDelegate = M;

if (myDelegate())
    Console.WriteLine(“Return value is true.”);
else
    Console.WriteLine(“Return value is false.”);

The next code snippet shows a call to a method that accepts two decimal numbers as input and returns a decimal number that represents the sum of both input parameters:

private decimal Sum(decimal n1, decimal n2)
{
    return n1 + n2;
}

Func<decimal, decimal, decimal> mySum = Sum;
Console.WriteLine(mySum(99.99M, 12.21M));

Anonymous methods and lambda expressions

You may use anonymous methods or lambda expressions in conjunction with the Func<> delegate.

  • Anonymous method:

Func<decimal, decimal, decimal> mySum = delegate(decimal n1, decimal n2) { return n1 + n2; };

Console.WriteLine(mySum(99.99M, 12.21M));

  • Lambda expression:

Func<decimal, decimal, decimal> mySum = (decimal n1, decimal n2) => n1 + n2;

Console.WriteLine(mySum(99.99M, 12.21M));

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