C# ref vs out in function/method parameter

1-ref.cs

string message = "hello";

public void SayMessage(ref string message) {
    Console.WriteLine(message);
    
    message = "hello in here";
}

SayMessage(ref message); // "hello"

Console.WriteLine(message); // "hello in here"

// run this code: http://csharppad.com/gist/ca901eb8e7d995a1f29c

2-out.cs

string message = "hello";

public void SayMessage(out string message) {
    message = "hello in here";
    
    Console.WriteLine(message);
}

SayMessage(out message); // "hello in here"

Console.WriteLine(message); // "hello in here"

// run this code: http://csharppad.com/gist/8e4c1dd9b153b3ef7d8f

3-out-wrong.cs

string message = "hello";

public void SayMessage(out string message) {
    Console.WriteLine(message); // (4,23): error CS0269: Use of unassigned out parameter 'message'
    
    message = "hello in here";
}

SayMessage(out message);

Console.WriteLine(message);

// run this code: http://csharppad.com/gist/8e4c1dd9b153b3ef7d8f

4-no-ref-out.cs

string message = "hello";

public void SayMessage(string message) {
    message = "hello in here";
    
    Console.WriteLine(message);
}

SayMessage(message); // "message"

Console.WriteLine(message); // "message"

// run this code: http://csharppad.com/gist/8e4c1dd9b153b3ef7d8f

@Rabbles glad to hear!