NP108 Declaring Objects

Question

Hi Guys

Usually when we declare an object, type and constructor method holds the same name. But in the following program it is not, please explain the reason.

Object someObject = new StringReader("This is a StringReader");

Thank you

using System;

using System.IO;

class MainClass

{

public static void Main()

{

Object someObject = new StringReader("This is a StringReader");

if (someObject is TextReader)

{

Console.WriteLine(

"is: someObject is a TextReader or a derived class");

}

/*

is: someObject is a TextReader or a derived class

*/

Maha · Answer

Thank you for your explanation.

Alan · Answer

Hey Maha thought I'd make another of my rare appearances :) The rules on implicit conversions are complicated but there's always an implicit conversion: 1. From any derived type to its parent (or an ancestor) type. 2. From any type to System.Object which is the ultimate parent of all types. 3. From any type to an interface type if the type implements the interface. It's also possible to create a user defined implicit conversion from one type to another. Finally there are implicit conversions defined between the numeric types. Broadly a type with a smaller range can be implicitly converted to a type with a larger range. So int can be converted to long and long can be converted to double without the need for a cast even though there's no inheritance relationship between these types.

Maha · Answer

According to your explanation name of some classes are subjected to implicit conversion. Is there any way to find out name of the classes available for implicit conversion?

Bechir Bejaoui · Answer

We call this class plymorphism it is implicit class conversion between classes. In your case may be a stream reader is boxed in an object and in order to unwrapp it and then use it we have to convert it implecitly to a stream reader object x = new streamReader(); it is also possible to convert classes implicitly like class1 x = new class2(); we use that in order to profit from the extended methods within the derived class but class2 should be derived type from class1 else and in the contrast case you will recieve a runtime error that indicates that the implicit conversion is impossible