Whether it is possible

Maha

http://www.c-sharpcorner.com/Forums/Thread/277334/constructor-body.aspx

I wish to know whether it is possible to do in the following program the way code is highlighted in the above web page. Problem is coloured.

using System;
public class CreateEmployee
{
public static void Main()
{
int id = 345;

Employee myAssistant = new Employee(id);

Console.WriteLine("ID # is {0}", myAssistant.GetId());

Console.ReadKey();
}
}
internal class Employee
{
private int idNumber;

public Employee(Employee myA)
{
idNumber = myA.idNumber;
}
public int GetId()
{
return idNumber;
}
}
// ID # is 345

9 Replies

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Vulpes11y ago
Accepted answer
It's incorrect because, as things stand, the Employee class does not define an explicit conversion to int.

However, it will work if you add the highlighted code:

using System;

public class CreateEmployee
{
public static void Main()
{
int id = 345;

Employee myAssistant = new Employee(id);

Console.WriteLine("ID # is {0}", myAssistant.GetId());

Employee myAssistant2 = new Employee(myAssistant);

Console.WriteLine("ID # is {0}", myAssistant2.GetId());

Console.ReadKey();
}
}

internal class Employee
{
private int idNumber;

public Employee(int id)
{
idNumber = id;
}

public Employee(Employee myA)
{
idNumber = (int)myA;
}

public int GetId()
{
return idNumber;
}

public static explicit operator int(Employee myA)
{
return myA.idNumber;
}
}

// ID # is 345
Maha11y ago
Thank you for your explanation.
Maha11y ago
This code is taken from the above program.

public Employee(Employee myA)
{
idNumber = myA.idNumber;
}

Why it is incorrect to write following way

public Employee(Employee myA)
{
idNumber = (int)myA;
}
Maha11y ago
Thank you for your help.
Michal Habalcik11y ago
Yep, I know, but you have to have at least one instance constructor available. I see you have added it so it runs just fine.
Vulpes11y ago
I think what you have in mind, Michal, is where you introduce a field (as opposed to a constructor parameter) of the same type as the enclosing class.

That certainly does create an infinite sequence of constructor calls leading to an out of memory exception.

However, copy constructors are OK - they're used in C++ all the time - and the code I posted above compiles and runs fine.
Vulpes11y ago
I've also just found an MSDN link on writing 'copy' constructors in C# which is worth reading:

http://msdn.microsoft.com/en-us/library/ms173116.aspx
Michal Habalcik11y ago
it won't even compile. You have just one constuctor with the Employee parameter, so giving it just pure int number won't work.

Also, the whole principle is just wrong. You can't use the class in its own constructor like this.

The constructor awaits the Employee and that Employee again awaits Employee in the constructor.

Something like:
```
Employee myAssistant = new Employee(new Employee(new Employee(and so on a on)))
```
Vulpes11y ago
Yes, it's perfectly possible to create one object from another of the same type using a 'copy' constructor.

I've altered your code to achieve it here:

using System;

public class CreateEmployee
{
public static void Main()
{
int id = 345;

Employee myAssistant = new Employee(id);

Console.WriteLine("ID # is {0}", myAssistant.GetId());

Employee myAssistant2 = new Employee(myAssistant);

Console.WriteLine("ID # is {0}", myAssistant2.GetId());

Console.ReadKey();
}
}

internal class Employee
{
private int idNumber;

public Employee(int id)
{
idNumber = id;
}

public Employee(Employee myA)
{
idNumber = myA.idNumber;
}

public int GetId()
{
return idNumber;
}
}
// ID # is 345