Optional Parameters in .Net

Optional Arguments were introduced in C# 4.0 and this article will show you how to use them. Optional Arguments are necessary when you specify functions that have a large number of arguments. It can cut down time by making you pass on argument values to the most needy parameters in a situation. 

Optional Arguments are what their name suggests i.e. even if you do not specify them, its perfectly OK. But it doesn't mean that they have not taken a value. In fact we specify some default values that the Optional Parameters take when values are not supplied in the function call. In this way we gain the functionality of easily setting values once and using these values several times as a default unless something different is needed. 

The values that we supply in the function Definition are some constants. Note that we can only supply one default value for one parameter. This makes sense as there can only be one default value for one property by definition. But this also means that multiple values cannot be assigned and given priorities in different situations. We have to check for ourselves which value fits in best in a given situation and supply it in a function call to that variable. These default values are to be used in case no value is supplied in the function call. These values are specified by typing in equations(with a single = sign) instead of just the declaration of variables.

For example, we write

static void Func(Str = "Default Value")

instead of static void Func(int Str)

If you didn't know this technique, you were probably using Function Overloading, but that technique requires multiple declaration of the same function. Using this technique you can define the function only once and have the functionality of multiple function declarations. 

Consider a function that is defined with two optional parameters. When only one parameter is supplied, the second parameter takes the default  value. We can then write the function in such a way as to check if the second parameter value received or not. If the parameter value is the default one then just ignore it and continue to work with the first parameter value. Thus we have the function overloading effect in which a same named function takes on two different tasks.  

When we supply two different parameters, the function works with both the values. This can be easily achieved using the if statement.  Just check which parameter has and does not have the default value. 

When using this technique it is best that you have declared optional & required parameters both. i.e. you can specify both types of parameters in your function declaration to get the most out of this technique.

An example of a function that uses both types of parameters is shown below:

static void Func(String Name, int Age, String Address = "N/A")

In the example above, Name & Age are required parameters. The string Address is optional, if not specified, then it would take the value "N/A" meaning the Address is not available.

For the above example, you could have two types of function calls:

  • Func("John Chow", 30, "America");

  • Func("John Chow", 30);

That's it from Optional Arguments. Have a look at Named Arguments for more information on parameter types.

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