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C# – Optional Arguments and Constructor Chaining

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Learned something new about C# today, first thing is Constructor Chaining.  Constructor chaining enables constructors to call another overloaded constructor, with it, the amount of duplicate code can be reduced significantly, here is an example:

class Person{
    string name;
    int age;
    string address;

    public Person(string name):this(string.Empty,0,string.Empty)
    {    }
    public Person(string name):this(name,0,string.Empty)
    {    }

    public Person(string name, int age):this(name,age,string.Empty)
    {    }

    public Person(string name, int age, string address)
    {
        this.name=name;
        this.age=age;
        this.address=address;
    }
}

// It can be used to call the base class' constructor as well, with the
// base keyword

class AwesomePerson:Person{
    int awesomenessLevel;

    public AwesomePerson(string name, int age, string address, int level):base(name,age,address)
    {
        this.awesomenessLevel = level;
    }

    public AwesomePerson(int level):this(string.Empty,0,string.Empty,level)
    {    }

// and so on...
}

With that, I can reduce the amount of code in the constructors, and still get the options of passing only the argument that I need to the constructors. There is another way to do this, starting with C# 4.0, it introduced optional arguments that is common in dynamic languages, and it is pretty awesome, and it can be combined with the constructors chaining above for more power!

class Person
{
    string name;
    int age;
    string address;

    public Person(string name = string.Empty,
                  int age=0,
                  string address = string.Empty)
    {
        this.name=name;
        this.age=age;
        this.address=address;
    }

}

// To create the instances:
Person a = new Person();
Person b = new Person("Joe");
Person c = new Person(age:19,address:"Somewhere");
Person c = new Person("John",23);

References:

This entry is posted in 2012.

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