Action as a optional parameter in a function

Question

Is it possible to have an Action as an optional parameter in a function? The button2Action should be optional.

public void DrawWindow(Rect p_PositionAndSize, string p_Button2Text = "NotInUse", Action p_Button2Action)
{
 // Stuff happens here
}

I tried it with e.g p_Button2Action = delegate{ Debug.Log("NotInUse"); } but it does not compile due to Default parameter value for p_Button2Action must be a compile-time constant. How do you make an optional Action that is a compile time constant?

Solution 1

You must specify a constant value for a default parameter, so the only default value you can specify for an Action is null.

However, it's easy to check for null and substitute the correct value:

public void DrawWindow(Rect p_PositionAndSize, string p_Button2Text = "NotInUse", Action p_Button2Action = null)
{
    if (p_Button2Action == null)
        p_Button2Action = delegate{ Debug.Log("NotInUse"); }

    ...
}

Solution 2

One workaround for this may be to just use classical overloading:

public void DrawWindow(Rect p_PositionAndSize, string p_Button2Text = "NotInUse")
{
    DrawWindow(p_PositionAndSize, delegate{ Thread.Sleep(1); }, p_Button2Text);
}

public void DrawWindow(Rect p_PositionAndSize, Action p_Button2Action, string p_Button2Text = "NotInUse")
{
 // Stuff happens here
}

This way you can specify the default action in the overload with two parameters.

Comments

[nemesv]

But OP wants to have a default action there like delegate{ Debug.Log("NotInUse"); } and not null

[vendettamit]

Then I think you should go with the Mario's suggestion. As per the language spec you can not use default value apart from null to reference types. only strings are allowed to have values in default parameters.

[RustemMazitov]

if you want null as default action you can use: p_Button2Action?.Invoke();

[Matthew Watson]

@RMazitov Note that the null coalescing operator is only available in C# 6 or later - so it's correct to use that now (but obviously it didn't exist in 2013)

[RustemMazitov]

yes, good point. thanks for bringing that up)