Writing a set extending ArrayList

[Guest]

I’m trying to write a Set class where it’s a list that you can add an element only once. So I naturally tried to extend the ArrayList and wrote this code. The problem is that it compiles but during execution it gives this error and points to the “if (!(this.Contains(value)))†line :
An unhandled exception of type 'System.StackOverflowException' occurred in mscorlib.dll

Here is my program:
public class Set : System.Collections.ArrayList
{
public Set()
{

}

public override int Add(object value)
{
int res;
if (!(this.Contains(value)))
{
res = this.Add(value);
}
else
{
res = this.IndexOf(value);
}
return res;
}
}

 

[Andy Gaskell]

the line res = this.Add(value); keeps calling your Add method recursively.

change the line to res = base.Add(value);

I'm trying to write a Set class where it's a list that you can add an

element only once. So I naturally tried to extend the ArrayList and wrote
this code. The problem is that it compiles but during execution it gives
this error and points to the "if (!(this.Contains(value)))" line :

 

[Kevin P. Fleming]

public override int Add(object value)
{
int res;
if (!(this.Contains(value)))
{
res = this.Add(value);

You need to use base.Add here, otherwise you're calling right back into
this Add method and will do so until the stack runs out of space.

 

[Guest]

Thanks. I’m coming from Java and was wondering about the ToString method. In Java whenever I wanted to check my collections, I could easily call its toString method and it would show the contents. In C# it seems they have not implemented a default ToString for each collection, right? Do I have to extend all the collections I need and override their ToString method?

 

[Jon Skeet [C# MVP]]

Thanks. I?m coming from Java and was wondering about the ToString
method. In Java whenever I wanted to check my collections, I could
easily call its toString method and it would show the contents. In C#
it seems they have not implemented a default ToString for each
collection, right? Do I have to extend all the collections I need and
override their ToString method?

I wouldn't bother doing that, myself. In the debugger you can just
expand them, and in code you can easily write a utilty method which
concatenates the result of calling ToString on each element.

 

[Guest]

I have also written a List class that extends ArrayList. How is it possible to convert a String [] to a List, or ArrayList elegantly? I know that you can do the reverse. I tired
List res = (List) List.Adapter((System.Collections.IList) tokenList.GetEnumerator());
tokenList is a String[]

It compiles but gives a runtime error. I can iterate throw the elements of the Array and add them to a new List but is it the only way?

 

[Jon Skeet [C# MVP]]

I have also written a List class that extends ArrayList. How is it
possible to convert a String [] to a List, or ArrayList elegantly? I
know that you can do the reverse. I tired List res = (List)
List.Adapter((System.Collections.IList) tokenList.GetEnumerator());
tokenList is a String[]

It compiles but gives a runtime error. I can iterate throw the
elements of the Array and add them to a new List but is it the only
way?

Arrays implement ICollection, so you can just use the constructor to
ArrayList which takes an ICollection parameter, assuming I understand
your question correctly.

 

[Guest]

Thanks! It didn’t work because I didn’t use this constructor in my new class
public List(System.Collections.ICollection c) : base(c

I’m now considering creating strongly typed Lists and Sets
I have Set that extends List and TextList that extends List
List <- Se
List <- TextLis

Now imagine if I want to create a TextSet. Should I extend Set or TextList? Unfortunately multiple inheritance is not allowed
List <- Set <- TextSe
o
List <- TextList <- TextSe

 

[Jon Skeet [C# MVP]]

Thanks! It didn?t work because I didn?t use this constructor in my new class.
public List(System.Collections.ICollection c) : base(c)

I?m now considering creating strongly typed Lists and Sets.
I have Set that extends List and TextList that extends List:
List <- Set
List <- TextList

Now imagine if I want to create a TextSet. Should I extend Set or
TextList? Unfortunately multiple inheritance is not allowed!
List <- Set <- TextSet
or
List <- TextList <- TextSet

And that's where you want to consider defining an ISet interface, and
make your class implement both IList and ISet - the actual
implementation derivation shouldn't matter too much.