How can I set default parameter value for an action

Question

How can I set default parameter value for an action when that parameter is dictionary type?

for example:

public void Test(Dictionary<int, bool> dic) {
    ...
}

Answer 1

You can't give it a default value the way you want to because it has to be a compile time constant value, but you can do something like this:

private static bool Test(Dictionary<string, string> par = null)
    {
        if(par == null) par = GetMyDefaultValue();
        // Custom logic here
        return false;
    }

Answer 2

You could use null as special case, like in other answers, but if you still want to be able to call Test(null) and have different behaviour to calling Test(), then you must chain overload:

public void Test(Dictionary<int, bool> dic) {
  //optional, stops people calling Test(null) where you want them to call Test():
  if(dic == null) throw new ArgumentNullException("dic");
...
}

public void Test() {
   var defaultDic = new Dictionary<int, bool>();
   Test(defaultDic);
}