C# creating my own class that acts like a string - C# Discussion Boards

Re: C# creating my own class that acts like a string

21-Jun-14 5:23

I am trying to create some classes that act like a string, but allow me to test the type at a later date. Because string and String are sealed, I can't seem to inherit from them. I also found out you can't override the assignment operator. I found something close to what I want here on stackoverflow, but it uses structs which can't be inherited. Here's a example of what I want to do, but I can't figure out how:

public class ORSerialLotNumber : string {}
public class SerialNumber : ORSerialLotNumber {}
public class LotNumber : ORSerialLotNumber {}

// ......

List<ORSerialLotNumber> mySLNList = new List<ORSerialLotNumber>();
SerialNumber sNum1 = "Sd-23s-3sf";
LotNumber nNum1 = "2342434";

mySLNList.Add(sNum1);
mySLNList.Add(nNum1);

// ......

foreach(var v in mySLNList)
    if(v.GetType() == typeof(SerialNumber))
        string serial = v;
    if(v.GetType() == typeof(LotNumber))
        string lot = v;

harold aptroot21-Jun-14 5:35

Re: C# creating my own class that acts like a string

21-Jun-14 5:35

That example doesn't really depend on it being a struct, it's about the implicit conversion operator.

Here's a minimal implementation of a class to implicitly converts to and from string:

class CustomString
{
    public static implicit operator CustomString(string s)
    {
        return new CustomString();
    }

    public static implicit operator string(CustomString s)
    {
        return "";
    }
}

Do that for both subclasses.

By the way, as far as I can tell you should be able to use is[^] instead of the GetType() == typeof() "not-quite-anti-pattern-but-close".

hpjchobbes21-Jun-14 17:20

Re: C# creating my own class that acts like a string

21-Jun-14 17:20

Thanks, this seems to be just what I need, though I imagine that I need to save the actual string value and have the constructor set that value and the operator string(CustomString s) return the string instead of an empty string?

class CustomString
{
    private string _value;

    private CustomString(string s)
    {
        _value = s;
    }
    
    public static implicit operator CustomString(string s)
    {
        return new CustomString(s);
    }

    public static implicit operator string(CustomString s)
    {
        return s._value;
    }
}

Would I also be able to implement INotifyPropertyChanged with this class? I don't see how as there's no public property. Would I just use "_value" even though it's private?

harold aptroot21-Jun-14 20:25

Re: C# creating my own class that acts like a string

21-Jun-14 20:25

You could just give it a public property though, right?

OriginalGriff21-Jun-14 20:29

OriginalGriff

21-Jun-14 20:29

There wouldn't be a whole lot of point in implementing the interface if he doesn't! Laugh | :laugh:

Those who fail to learn history are doomed to repeat it. --- George Santayana (December 16, 1863 – September 26, 1952)
Those who fail to clear history are doomed to explain it. --- OriginalGriff (February 24, 1959 – ∞)

Re: C# creating my own class that acts like a string

hpjchobbes22-Jun-14 7:24

Re: C# creating my own class that acts like a string

22-Jun-14 7:24

So the idea would be to include a public property, but still have the implicit operator act on that property? Would that then allow someone to either use the implicit operator or the property directly?

harold aptroot22-Jun-14 7:29

Re: C# creating my own class that acts like a string

22-Jun-14 7:29

Yes, is it giving you any trouble?

hpjchobbes22-Jun-14 9:52

Re: C# creating my own class that acts like a string

22-Jun-14 9:52

No, I just didn't even think about this, or even know that it was possible. I'm reading more about `implicit`, which seems very useful. It doesn't seem to be touched on in most 'beginner' reading, though.

BobJanova23-Jun-14 1:26

BobJanova

23-Jun-14 1:26

I'm not quite sure what you're trying to achieve here. I think it is that you want a data object that has a 'number' (a string identifier) and also a type. Using GetType or is/as functions is generally a sign that you haven't quite got the solution you want; switching based on type usually implies you need more polymorphic behaviour.

I think the better solution is

enum ItemType { Serial, Lot };
struct ObjectIdentifier {
 string Identity { get; set; }
 ItemType Type { get; set; }
}

List<ObjectIdentifier> mySLNList = ...;

foreach(ObjectIdentifier oi in mySLNList)
 switch(oi.Type)
  ...

please recommend a book for beginner

solo920-Jun-14 13:10

20-Jun-14 13:10

What would a good book to start learning C#? I'm not looking for theory and such, but more of practical use of code. There are SO MANY and don't know which/how to choose.
Thanks

Peter Leow20-Jun-14 16:12

Peter Leow

20-Jun-14 16:12

Check these out:
1. csharp-books-for-absolute-beginner[^]
2. Useful Reference Books[^]

solo920-Jun-14 16:23

20-Jun-14 16:23

Thanks.
Would this book be ok? http://www.amazon.ca/Microsoft-Visual-2013-Step-Developer-ebook/dp/B00JDMPO7K/ref=sr_1_1?s=books&ie=UTF8&qid=1403317347&sr=1-1&keywords=step+by+step+visual+c%23[^]

Peter Leow20-Jun-14 16:36

Peter Leow

20-Jun-14 16:36

According to the review[^], it should be fine.

OriginalGriff20-Jun-14 19:03

OriginalGriff

20-Jun-14 19:03

Pretty much any of them, provided they don;t have multiple exclamation marks, "in xxx days", or "for dummies" in the title. Wrox do good ones, and so do Adison-Wesley.
This is a good one: Pro C# 5.0 and the .Net 4.5 Framework[^] - I started with the .NET 2.0 version and it's pretty easy to follow.

If you want "practical use of code" then you need to concentrate on the .NET framework rather than the language: if you have a good grounding in other non-Net languages, then you can pick up pretty much the whole of C#-the-language in an afternoon. The .NET framework on the other hand is months of learning - and you can't use C# effectively without it.

solo921-Jun-14 1:44

21-Jun-14 1:44

Thanks. But that book says it's intended NOT for beginners...

harold aptroot21-Jun-14 2:06

21-Jun-14 2:06

Then read the book, you won't be a beginner anymore so you can read the book.

OriginalGriff21-Jun-14 2:26

OriginalGriff

21-Jun-14 2:26

Depends what you are a beginner in! Laugh | :laugh:

If this is your first computing language, then no, it isn't suitable - but then you'd be silly to ignore the theory because you need that to make the "practical use of code" understandable in a wider context.

Computing isn't like cooking: you don't just follow a recipe, you have to understand what the ingredients do, and why you want to use rice flour instead of strong white bread flour, for example. If you don't understand that, then you will use the wrong ingredient and produce something that is only technically food...or code that is only technically an application! Wink | ;)

solo921-Jun-14 11:29