Is there a way to specify an "empty" C# lambda expression?

Question

I'd like to declare an "empty" lambda expression that does, well, nothing. Is there a way to do something like this without needing the DoNothing() method?

public MyViewModel()
{
    SomeMenuCommand = new RelayCommand(
            x => DoNothing(),
            x => CanSomeMenuCommandExecute());
}

private void DoNothing()
{
}

private bool CanSomeMenuCommandExecute()
{
    // this depends on my mood
}

My intent in doing this is only control the enabled/disabled state of my WPF command, but that's an aside. Maybe it's just too early in the morning for me, but I imagine there must be a way to just declare the x => DoNothing() lambda expression in some way like this to accomplish the same thing:

SomeMenuCommand = new RelayCommand(
    x => (),
    x => CanSomeMenuCommandExecute());

Is there some way to do this? It just seems unnecessary to need a do-nothing method.

Rauhotz · Accepted Answer · 2009-11-16 15:48:52Z

295

Action doNothing = () => { };

answered Nov 16, 2009 at 15:48

Rauhotz

8,1806 gold badges43 silver badges45 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

qqqqqqq Over a year ago

Does there exist a predefined empty lambda? I think that it is a bad idea performance wise to create an empty lambda every time I need it. E.g. in JQuery there is the noop and I would expect something similar to be present in C#.

Patrick Szalapski Over a year ago

So is an async version of this require the verbose Func<Task> doNothing = async() => await Task.CompletedTask;?

StayOnTarget · Accepted Answer · 2020-10-14 13:09:01Z

27

I thought I would add some code that I've found useful for this type of situation. I have an Actions static class and a Functions static class with some basic functions in them:

public static class Actions
{
  public static void Empty() { }
  public static void Empty<T>(T value) { }
  public static void Empty<T1, T2>(T1 value1, T2 value2) { }
  /* Put as many overloads as you want */
}

public static class Functions
{
  public static T Identity<T>(T value) { return value; }

  public static T0 Default<T0>() { return default(T0); }
  public static T0 Default<T1, T0>(T1 value1) { return default(T0); }
  /* Put as many overloads as you want */

  /* Some other potential methods */
  public static bool IsNull<T>(T entity) where T : class { return entity == null; }
  public static bool IsNonNull<T>(T entity) where T : class { return entity != null; }

  /* Put as many overloads for True and False as you want */
  public static bool True<T>(T entity) { return true; }
  public static bool False<T>(T entity) { return false; }
}

I believe this helps improve readability just a tiny bit:

SomeMenuCommand = new RelayCommand(
        Actions.Empty,
        x => CanSomeMenuCommandExecute());

// Another example:
var lOrderedStrings = GetCollectionOfStrings().OrderBy(Functions.Identity);

edited Oct 14, 2020 at 13:09

StayOnTarget

13.4k11 gold badges66 silver badges117 bronze badges

answered Dec 28, 2012 at 15:17

Anthony

9,6119 gold badges49 silver badges75 bronze badges

4 Comments

Avrohom Yisroel Over a year ago

I wish I could upvote this again!

Sam Rueby Over a year ago

Can you verify that this only creates one instance of an Action? I.e. calling the generic Actions.Empty twice (given the same delegate type) creates only one instance rather than two?

Ackdari Over a year ago

This will create more objects than needed (example)

Jeremy Lakeman Mar 18 at 4:57

In C#11 the compiler will reuse static delegate instances in more cases, but you still need to be careful to avoid extra allocations (see devblogs.microsoft.com/dotnet/…)

Joseph · Accepted Answer · 2009-11-16 15:48:11Z

10

This should work:

SomeMenuCommand = new RelayCommand(
    x => {},
    x => CanSomeMenuCommandExecute());

answered Nov 16, 2009 at 15:48

Joseph

25.6k8 gold badges83 silver badges129 bronze badges

Comments

Jon Skeet · Accepted Answer · 2009-11-16 17:41:32Z

7

Assuming you only need a delegate (rather than an expression tree) then this should work:

SomeMenuCommand = new RelayCommand(
        x => {},
        x => CanSomeMenuCommandExecute());

(That won't work with expression trees as it's got a statement body. See section 4.6 of the C# 3.0 spec for more details.)

edited Nov 16, 2009 at 17:41

answered Nov 16, 2009 at 15:47

Jon Skeet

1.5m893 gold badges9.3k silver badges9.3k bronze badges

Comments

Jorge Córdoba · Accepted Answer · 2009-11-16 15:49:08Z

3

I don't fully understand why do you need a DoNothing method.

Can't you just do:

SomeMenuCommand = new RelayCommand(
                null,
                x => CanSomeMenuCommandExecute());

answered Nov 16, 2009 at 15:49

Jorge Córdoba

52.4k11 gold badges83 silver badges130 bronze badges

5 Comments

Dykam Over a year ago

That is probably checked and will probably throw a NRE.

Rob Over a year ago

I think Dykam is right, but I just didn't think about passing null :-)

Cohen Over a year ago

I don't understand why this is downvoted? Jorge makes a valid point, although it would have been a small effort to check it.

nawfal Over a year ago

+1, this is a valid solution, just that the null checking should be extended in new RelayCommand(...

Tom Over a year ago

Imagine what you would need to do in the method using that "null" Action....checking if (action == null) action(); every time.

Olivier Jacot-Descombes · Accepted Answer · 2025-03-17 18:10:25Z

3

Starting with C# 9.0 you can specify discards _ for required parameters. Example:

Action<int, string, DateTime> doNothing = (_, _, _) => { };

edited Mar 17 at 18:10

answered Jan 30, 2023 at 14:38

Olivier Jacot-Descombes

114k14 gold badges149 silver badges202 bronze badges

Comments

Javi Kroonenburg · Accepted Answer · 2020-11-21 09:28:30Z

0

Action DoNothing = delegate { };
Action DoNothing2 = () => {};

I used to initialize Events to a do nothing action so it was not null and if it was called without subscription it would default to the 'do nothing function' instead of a null-pointer exception.

public event EventHandler<MyHandlerInfo> MyHandlerInfo = delegate { };

edited Nov 21, 2020 at 9:28

answered Nov 21, 2020 at 9:20

Javi Kroonenburg

1,1208 silver badges11 bronze badges

Collectives™ on Stack Overflow

Is there a way to specify an "empty" C# lambda expression?

7 Answers 7

2 Comments

4 Comments

Comments

Comments

5 Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

7 Answers 7

2 Comments

4 Comments

Comments

Comments

5 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related