How do I know the default value is used?

Question

Consider a method like this:

public void WorkAt(string location = @"home")
{
    //...
}

It can be called by passing a value explicitly, like:

WorkAt(@"company");
WorkAt(@"home");

Or just use the default value, like:

WorkAt();

Is there a way to know whether the default value is used?

For example, I want to code like this:

public void WorkAt(string location = @"home")
{
     if ( /* the default value is used unexplicitly */)
     {
         // Do something
     }
     else
     {
         // Do another thing
     }
}

Be careful that WorkAt("home") is different from WorkAt() in this context.

Answer 1

There is not, and should not be, any reason to do this. The default value is there to do just that - provide a default value when none is specified.

If you need to perform a different function based on what is passed, I suggest overloading the method. For example:

public void WorkAt()
{
    //do something
}

public void WorkAt(string location)
{
    //do other thing
}

Alternatively, if there is shared logic, you could use an additional parameter:

public void WorkAt(string location = "home", bool doOtherThingInstead = false)
{
    if (!doOtherThingInstead)
    {
        //do something
    }
    else
    {
        //do other thing
    }

    //do some shared logic for location, regardless of doOtherThingInstead
}

As a side note, perhaps the example in the question was contrived, but WorkAt() with no parameter specified makes no lexical sense. One would expect a value after the word at. Perhaps you may want to rename the second method WorkAtDefaultLocation().

Answer 2

Your answer might be something like the following code.

public void CommonOperations(/*Some parameteres as needed.*/)
{
    // Shared operations between two methods.
}
public void WorkAt()
{
    string location = "home";
    CommonOperations(/*Some parameteres as needed.*/);
    //do something
}

public void WorkAt(string location)
{
    CommonOperations(/*Some parameteres as needed.*/);
    //do the other thing
}

I hope it will help.

Answer 3

You can use ReferenceEquals for this purpose.

However the string you are sending should not be a compile time constant, otherwise string "home" has the same reference with default value "home" and will return true. Why?

In order to create a string with a different reference you have to make a deep copy from that string.

    static void Main()
    {
        WorkAt(); // Prints true
        WorkAt("home"); // Prints true because the string is a compile-time constant

        // DeepClone before passing parameter to WorkAt.
        WorkAt(DeepClone("home"));// Prints false for any string.
    }

    static void WorkAt(string location = @"home")
    {
        if (ReferenceEquals(location, @"home")) // Only true when using default parameter
        {
            Console.WriteLine(true);
        }
        else
        {
            Console.WriteLine(false);
        }
    }

    static string DeepClone(string str) // Create a deep copy
    {
         return new string(str.ToCharArray());
    }

Note that this is the only way to understand if the default value is used or not. because the default value is always compile-time constant but the parameter sent to the method is not.

BTW as @lc. explained there is actually no reason to do this since you can use method overloads.

Answer 4

Use a sentinel value instead of the default

public void WorkAt(location="default_sentinel_value") {
    if (location == "default_sentinel_value") {
        location = "home";
        ...
    }
    else
    {
        ...
    }
}

Answer 5

As a programmer, the default value is a known value, so you can code like any of the following methods:

Method 1:

public void WorkAt(string location = @"home")
{
    if (location == @"home")
    {
        // Do something
    }
    else
    {
        // Do another thing
    }
}

Method 2: Make use of function Over loading

//function(A) with default value
public static void samplemethod()
    {
       string defaultValue="home";
       //Do something
    }

//function (B) without default value
public static void samplemethod(string x)
    {
         //Do something
    }

Then samplemethod("someValue"); will call function(B) and samplemethod(); will call function(A)

Answer 6

If you use OO, you can just create some GetSet property.

private string pvt_default;
private string pvt_location;
public string location
{
    get
    {
        return this.pvt_location;
    }
    set
    {
        if (pvt_default == location)
        {
            // do somthing
        }
        this.pvt_location = location;
    }
}

Answer 7

Change default value to null and change it to @"home"