Delegates and Lambdas

Passing Delegates

A helper method can receive a delegate and call it.

callback A callback is callable behavior passed into another method.

Passing Delegates

factor
PassingDelegates.cs
Replay: real traced execution (multi-file project)
using System;

class Program
{
    static int Apply(int value, Func<int, int> transform)
    {
        return transform(value);
    }

    static void Main()
    {
        int factor = 3;
        Func<int, int> multiply = value => value * factor;
        int result = Apply(5, multiply);

        Console.WriteLine($"factor={factor}");
        Console.WriteLine($"result={result}");
    }
}

using System;

class Program
{
    static int Apply(int value, Func<int, int> transform)
    {
        return transform(value);
    }

    static void Main()
    {
        int factor = 2;
        Func<int, int> multiply = value => value * factor;
        int result = Apply(5, multiply);

        Console.WriteLine($"factor={factor}");
        Console.WriteLine($"result={result}");
    }
}

using System;

class Program
{
    static int Apply(int value, Func<int, int> transform)
    {
        return transform(value);
    }

    static void Main()
    {
        int factor = 4;
        Func<int, int> multiply = value => value * factor;
        int result = Apply(5, multiply);

        Console.WriteLine($"factor={factor}");
        Console.WriteLine($"result={result}");
    }
}

  1. factor ← 3, multiply ← System.Func`2[System.Int32,System.Int32]

    10static void Main()11{12    int factor→ 3 = 3; //@factor=2, 413    Func<int, int> multiply→ System.Func`2[System.Int32,System.Int32] = value => value * factor;14    int result = Apply(5, multiplySystem.Func`2[System.Int32,System.Int32]);

  2. static int Apply(int value, Func<int, int> transform)

    4{5    static int Apply(int value5, Func<int, int> transformSystem.Func`2[System.Int32,System.Int32])6    {7        return transform(value5);8    }

  3. result ← 15

    13    Func<int, int> multiply = value => value * factor;14    int result→ 15 = Apply(5, multiplySystem.Func`2[System.Int32,System.Int32]);1516    Console.WriteLine($"factor={factor3}");17    Console.WriteLine($"result={result15}");18}
    outputfactor=3
result=15

  1. factor ← 2, multiply ← System.Func`2[System.Int32,System.Int32]

    10static void Main()11{12    int factor→ 2 = 2;13    Func<int, int> multiply→ System.Func`2[System.Int32,System.Int32] = value => value * factor;14    int result = Apply(5, multiplySystem.Func`2[System.Int32,System.Int32]);

  2. static int Apply(int value, Func<int, int> transform)

    4{5    static int Apply(int value5, Func<int, int> transformSystem.Func`2[System.Int32,System.Int32])6    {7        return transform(value5);8    }

  3. result ← 10

    13    Func<int, int> multiply = value => value * factor;14    int result→ 10 = Apply(5, multiplySystem.Func`2[System.Int32,System.Int32]);1516    Console.WriteLine($"factor={factor2}");17    Console.WriteLine($"result={result10}");18}
    outputfactor=2
result=10

  1. factor ← 4, multiply ← System.Func`2[System.Int32,System.Int32]

    10static void Main()11{12    int factor→ 4 = 4;13    Func<int, int> multiply→ System.Func`2[System.Int32,System.Int32] = value => value * factor;14    int result = Apply(5, multiplySystem.Func`2[System.Int32,System.Int32]);

  2. static int Apply(int value, Func<int, int> transform)

    4{5    static int Apply(int value5, Func<int, int> transformSystem.Func`2[System.Int32,System.Int32])6    {7        return transform(value5);8    }

  3. result ← 20

    13    Func<int, int> multiply = value => value * factor;14    int result→ 20 = Apply(5, multiplySystem.Func`2[System.Int32,System.Int32]);1516    Console.WriteLine($"factor={factor4}");17    Console.WriteLine($"result={result20}");18}
    outputfactor=4
result=20