Delegates and Lambdas

Func and Action

Func returns a value, while Action performs work without returning one.

Func and Action `Func` delegates return values, and `Action` delegates return `void`.

Func and Action

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

class Program
{
    static void Main()
    {
        string word = "ready";
        Func<string, string> bracket = text => "[" + text + "]";
        string output = "";
        Action<string> save = text => output = text;

        save(bracket(word));

        Console.WriteLine($"word={word}");
        Console.WriteLine($"output={output}");
    }
}

using System;

class Program
{
    static void Main()
    {
        string word = "done";
        Func<string, string> bracket = text => "[" + text + "]";
        string output = "";
        Action<string> save = text => output = text;

        save(bracket(word));

        Console.WriteLine($"word={word}");
        Console.WriteLine($"output={output}");
    }
}

using System;

class Program
{
    static void Main()
    {
        string word = "start";
        Func<string, string> bracket = text => "[" + text + "]";
        string output = "";
        Action<string> save = text => output = text;

        save(bracket(word));

        Console.WriteLine($"word={word}");
        Console.WriteLine($"output={output}");
    }
}

  1. word ← ready, bracket ← System.Func`2[System.String,System.String]

    4{5    static void Main()6    {7        string word→ ready = "ready"; //@word="done", "start"8        Func<string, string> bracket→ System.Func`2[System.String,System.String] = text => "[" + text + "]";9        string output→ (empty) = "";10        Action<string> save→ System.Action`1[System.String] = text => output = text;1112        save(bracket(wordready));1314        Console.WriteLine($"word={wordready}");15        Console.WriteLine($"output={output[ready]}");16    }
    outputword=ready
output=[ready]

  1. word ← done, bracket ← System.Func`2[System.String,System.String]

    4{5    static void Main()6    {7        string word→ done = "done";8        Func<string, string> bracket→ System.Func`2[System.String,System.String] = text => "[" + text + "]";9        string output→ (empty) = "";10        Action<string> save→ System.Action`1[System.String] = text => output = text;1112        save(bracket(worddone));1314        Console.WriteLine($"word={worddone}");15        Console.WriteLine($"output={output[done]}");16    }
    outputword=done
output=[done]

  1. word ← start, bracket ← System.Func`2[System.String,System.String]

    4{5    static void Main()6    {7        string word→ start = "start";8        Func<string, string> bracket→ System.Func`2[System.String,System.String] = text => "[" + text + "]";9        string output→ (empty) = "";10        Action<string> save→ System.Action`1[System.String] = text => output = text;1112        save(bracket(wordstart));1314        Console.WriteLine($"word={wordstart}");15        Console.WriteLine($"output={output[start]}");16    }
    outputword=start
output=[start]