How can you use optional parameters in C#?

Question

^{Note: This question was asked at a time when C# did not yet support optional parameters (i.e. before C# 4).}

We\'re building a web API tha

Answer 1

optional parameters are for methods. if you need optional arguments for a class and you are:

• using c# 4.0: use optional arguments in the constructor of the class, a solution i prefer, since it's closer to what is done with methods, so easier to remember. here's an example:

  class myClass
  {
      public myClass(int myInt = 1, string myString =
                             "wow, this is cool: i can have a default string")
      {
          // do something here if needed
      }
  }
  

• using c# versions previous to c#4.0: you should use constructor chaining (using the :this keyword), where simpler constructors lead to a "master constructor". example:

  class myClass
  {
      public myClass()
      {
      // this is the default constructor
      }
  
      public myClass(int myInt)
          : this(myInt, "whatever")
      {
          // do something here if needed
      }
      public myClass(string myString)
          : this(0, myString)
      {
          // do something here if needed
      }
      public myClass(int myInt, string myString)
      {
          // do something here if needed - this is the master constructor
      }
  }
  

Answer 2

I have a web service to write that takes 7 parameters. Each is an optional query attribute to a sql statement wrapped by this web service. So two workarounds to non-optional params come to mind... both pretty poor:

method1(param1, param2, param 3, param 4, param 5, param 6, param7) method1(param1, param2, param3, param 4, param5, param 6) method 1(param1, param2, param3, param4, param5, param7)... start to see the picture. This way lies madness. Way too many combinations.

Now for a simpler way that looks awkward but should work: method1(param1, bool useParam1, param2, bool useParam2, etc...)

That's one method call, values for all parameters are required, and it will handle each case inside it. It's also clear how to use it from the interface.

It's a hack, but it will work.

Answer 3

Surprised no one mentioned C# 4.0 optional parameters that work like this:

public void SomeMethod(int a, int b = 0)
{
   //some code
}

Edit: I know that at the time the question was asked, C# 4.0 didn't exist. But this question still ranks #1 in Google for "C# optional arguments" so I thought - this answer worth being here. Sorry.

Answer 4

In C#, I would normally use multiple forms of the method:

void GetFooBar(int a) { int defaultBValue;  GetFooBar(a, defaultBValue); }
void GetFooBar(int a, int b)
{
 // whatever here
}

UPDATE: This mentioned above WAS the way that I did default values with C# 2.0. The projects I'm working on now are using C# 4.0 which now directly supports optional parameters. Here is an example I just used in my own code:

public EDIDocument ApplyEDIEnvelop(EDIVanInfo sender, 
                                   EDIVanInfo receiver, 
                                   EDIDocumentInfo info,
                                   EDIDocumentType type 
                                     = new EDIDocumentType(EDIDocTypes.X12_814),
                                   bool Production = false)
{
   // My code is here
}

Answer 5

I agree with stephenbayer. But since it is a webservice, it is easier for end-user to use just one form of the webmethod, than using multiple versions of the same method. I think in this situation Nullable Types are perfect for optional parameters.

public void Foo(int a, int b, int? c)
{
  if(c.HasValue)
  {
    // do something with a,b and c
  }
  else
  {
    // do something with a and b only
  }  
}

Answer 6

Using overloads or using C# 4.0 or above

 private void GetVal(string sName, int sRoll)
 {
   if (sRoll > 0)
   {
    // do some work
   }
 }

 private void GetVal(string sName)
 {
    GetVal("testing", 0);
 }