Casting...

Hi there,

I'm in the throws of learning C#, but I am currently trying to figure out why I would use casting with reference types. From what I understand, casting is used to convert one type to another (please correct me if I am wrong), and I understand this concept when using primitive data types. What I am struggling to understand is why you would use casting when dealing with reference types.

I've checked various sites, but none of them offer a clear understanding of why you would cast one object to another.

Am I missing something fundamental to OOP?

Any help would be gratefully received.

Well, the variable (in C#, 99 % of the variables are a "pointer" to a referenced object) is of a specific object.

In C++, you also cast a pointer to a specific type if you want to call its functions. In C#, it works exactly the same. You need to convert the object to the right type so you can call the right functions on it.

Quote:

---

Originally Posted by Tischnoetentoet

Well, the variable (in C#, 99 % of the variables are a "pointer" to a referenced object) is of a specific object.

In C++, you also cast a pointer to a specific type if you want to call its functions. In C#, it works exactly the same. You need to convert the object to the right type so you can call the right functions on it.

---

Many thanks for your response.

Do you have any recommended web-sources that give a thorough explanation?

Again, thanks for your help.

All types in C# derive from object. Some methods operate in a generic fashion and return an object that must be cast to the desired type.

For example, consider the System.Enum.Parse method which returns an object. Given a string and an enum type, this method returns an object that can be cast to the enum type (with the string represented as an enum value).

Code:

---

enum Color { Red, Green, Blue };

Color color = (Color) Enum.Parse( typeof( Color ), "Green" );

// The value of color is 'Color.Green'.

---

In the above snippet, you would get an 'unable to convert type' error if you tried the following without the cast:

Code:

---

Color color = Enum.Parse( typeof( Color ), "Green" );

---

Read more in Casting (C# Programming Guide).

As personal preference, I generally try to avoid casting as much as possible in my code. As such I rarely pass objects to and from methods.

Quote:

---

Originally Posted by Arjay

As personal preference, I generally try to avoid casting as much as possible in my code. As such I rarely pass objects to and from methods.

---

How do you manage this in C# where everything derives from System.Object :confused: lol.

Also, C# has a nice little sugar syntax tweak that allows you to do this:

Code:

---

enum Color { Red, Green, Blue };

Color color =  Enum.Parse( typeof( Color ), "Green" ) as Color;

// The value of color is 'Color.Green'.

---

Notice the "as Color" syntax on the end. I never use it, Im more partial to the C++ way but some developers might find it handy.

EDIT:

Oops, I forgot color was a VALUE type, therefore casting from a reference type to a value type does NOT work with the "as" syntax sugar. However, any reference type to reference type casts will work with it.

Quote:

---

Originally Posted by Arjay
As personal preference, I generally try to avoid casting as much as possible in my code. As such, I rarely pass objects to and from methods.

---

Quote:

---

Originally Posted by RaleTheBlade

How do you manage this in C# where everything derives from System.Object :confused: lol.

---

Because I avoid passing objects in my methods.

For example, I tried to avoid doing this:

Code:

---

void Method( object obj );

---

If a method or class can operate on multiple types, I'll use generics.

Passing raw objects is always a last resort (just like I didn't like to pass void* in C++).

Thanks for the responses, guys. Very much appreciated! :thumb: