Is this design okay in C#

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1.00/5 (1 vote)

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Just wondering if this is "good practice" or not. I want to create a Token class that can hold a string or an integer, and process tokens of either type. I have looked at open generics, generics, abstracts, overriding etc. and chose simple solution below:-

C#

using System.IO;
using System;

public class Token 
{
    public dynamic Value {get; set;}
}

class Program
{
    static void Main()
    {   
        Token token1;
        Token token2; 
    
        token1 = new Token();
        token2 = new Token();
        
        token1.Value=1;
        token2.Value="hi";
        Console.WriteLine(token1.Value);
        Console.WriteLine(token2.Value);
        token1.Value=token2.Value;
        Console.WriteLine(token1.Value);
        Console.WriteLine(token2.Value);
    }
}

What I have tried:

?? as above - not sure what to put here ?

Posted 16-May-17 23:48pm

ninjaef

Updated 17-May-17 1:30am

Kornfeld Eliyahu Peter

v2

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F-ES Sitecore 17-May-17 7:03am

You're probably better going down the generics route. It's rare that you'll never really care about the type in question, and if all you're doing is printing the value to a console or log etc then you can have a base generic class and concerete classes that inherit that base class which provide their own ToString implementations

abstract class MyBaseClass<t>
{
public T Value {get; set;}
abstract string ToString();
}

class IntClass : MyBaseClass<int>
{
public string ToString()
{
return Value.ToString();
}
}

That lets you use any type and each concrete class can then provide its own implementation of ToString as you may want "T" to be a class like Person with complex properties.

ninjaef 17-May-17 8:52am

I like this. It also consistent with base/simple types (int, int32, ...) not sure what you call them. Thanks. But, how do I declare an object of MyBaseClass and call .Value for both?

ninjaef 17-May-17 8:58am

okay, but how do I declare an object to receive a token:

MyBaseClass token; //wouldnt compile?
...
...
token = getNextToken() // could return a string or an int

if <<token is int>> then ... else <<token is string>> ...

???

F-ES Sitecore 17-May-17 9:36am

You would have to work with the specific derived concrete type or MyBaseClass<int> for example. Or have the class that needs to use getNextToken be a generic class also. There is no real way of handling completely type-agnostic data, you have to specify a type at some point, or have getNextToken return a fixed type such as a string, or an object but again the calling code needs to know what type to cast to. You have to think about the problem you're actually trying to solve, .net is a compiled language so it doesn't really have the concept of non-defined types.

ninjaef 17-May-17 9:57am

the original ...

public class Token
{
public dynamic Value {get; set;} //compiles
}
Token mytoken = GetNextToken() // works runtime ; token.Value could yield an (int) or a (char) etc

if mytoken.Type = INTEGER then <<treat as int>> else <<treat as char>>

// so polymorphism?

...

as I say, all works as required, arguably easier than your solution, but I was wondering whether my solution was good practice - clearly its allowed in C# and compiles/runs

??

F-ES Sitecore 17-May-17 10:10am

Personally I would say it isn't good design to use dynamic. You still haven't really explained your ultimate intention so it's hard to give specific advice. The only thing on use you can really do with something whose type you never know is to convert it to a string so you may as well use string as your token and get the code that creates the token to convert the token to a string.

ninjaef 17-May-17 10:17am

pretty self explanatory , as above , I am writing a parser and this includes a tokenizer. each token is read (getnexttoken) where the type (int, char, string, other) is determined at runtime because the token definition is a text file with regex clauses, i.e.

ALPHA=[a-z|A-Z]
DIGIT=[0-9]
INTEGER = DIGIT+
IDENTIFIER = ALPHA (ALPHA | DIGIT)+

etc

so at run time, a token type is as per defined by the grammar

so I want to be able to define a "generic" class where the Value can be interpreted at run time. dynamic sort of models untyped langauges such as python etc.

not good as you say, in C#, I agree, but the compiler lets you do it and the CLR lets you run it!

?

F-ES Sitecore 17-May-17 10:20am

In that situation you could look at the factory pattern would would analyse the token and return a class of the correct type for that token. Again it all comes down to how you actually comsume the token.

ninjaef 17-May-17 10:28am

interesting, could you explain / example please?
EDIT: tokens are consumed as chars, as per the grammar I outlined above, and then converted to int if they are INTEGER (as per code above) etc.

F-ES Sitecore 17-May-17 10:34am

https://www.dotnetperls.com/factory

For you the Factory.Get will take the token and depending on its type return the specific concrete class for the token.

ninjaef 17-May-17 10:42am

ah. perfect! and better solution than mine as you use compile time type-safe logic. MANY THANKS!

ninjaef 17-May-17 11:56am

ah, hang on
actually
that's not what I need.
in your example, Title prop, i woould want Value prop that either returns a string for a IDENTIFIER token, or an int for an INTEGER token
not quite the same as the example
and
coming from C language, I'm not sure how to do this

F-ES Sitecore 17-May-17 12:00pm

As I keep saying and you haven't answered, the solution will depend on what reads the value, ie what you ultimately do with it. If all that happens is that it is written to a log or the screen then just use a string, if you do something intelligent with it then I can't see how you can do anything of value with something whose type you don't know.

ninjaef 17-May-17 14:00pm

this is it!

terface by now:

public interface IProperty
{
public String Name { get; }
}

public class Property<t> : IProperty
{
public Property(String name, T value)
{
Name = name;
Value = value;
}

public String Name { get; private set; }
public T Value { get; private set; }

public override String ToString()
{
return string.Format("{0}: {1}", Name, Value)
}
}

...

var intProp = new Property<int> ("age", 32);
var strProp = new Property<string> ("name", "Earl");
var enumProp = new Property<colorenum> ("eye color", ColorEnum.Magenta);

but i dont really understand what's going on, despite me reading msdn and online

F-ES Sitecore 18-May-17 4:08am

When you define the class;

var intProp = new Property<int>();

then whatever you put in the angled brakcets (int in the above example) is what "T" becomes, so your interface properties are really

public String Name { get; private set; }
public int Value { get; private set; }

so intProp.Value is an int but strProp.Value is a string, you are deciding the type that "T" becomes when you declare\create the class. One thing to note, however, is to not be fooled by the "var" element. var isn't a general variable that can contain anything, it is simply a "macro" where var is replace by the proper type by your compiler so your code is really

Property<int> intProp = new Property<int>();
Property<string> strProp = new Property<string>();

in other words, intProp and strProp are not interchangable and cannot be dynamically allocated at runtime, you still need to know what type they have to be.

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OriginalGriff · Answer 1 · 2017-05-17T00:05:00

It depends what you want to do with it. Probably, I'd create an abstract Token class, and derive more concrete classes from that to represent what teh token types are supposed to do, or be used for:

C#

public class TokenNumber: Token ...
public class TokenUserName: Token ...

I'd then add abstract processing methods which each derived class has to implement. It's possible that this might be an Interface rather than an abstract class, but that would depend on what else you need to do with your Tokens.
Using a Dynamic variable as you are is basically the same as using an object:

public class Token 
{
    public object Value {get; set;}
}

Which defeats the strong typing that is one of the reasons C# is so much better than VB.

ninjaef · Answer 2 · 2017-05-17T01:30:00

Solution 2

Using your solution, the read/write to/from Value would require a cast

...
public object Value {get; set;}
...
(int)Value
(string)Value

??

Posted 17-May-17 1:30am