Building an object with a [] interface ( not from ILIst) in c#

Question

I want to pass around some values in an array that will always be a known size. I would like to define a class that represents this array of decimal values which could not be resized, would always have the same number of elements, and supports the [] array notation.

In c++ I could do an operator overloading for this - but I can't see how to do it in c#

To be clear - the use of the class would be something like:

MyValues values = new MyValues;
values[3] = 14;
values[7] = 10

.... And later

decimal aValue = values[2];

Suggestions?

@Mike: `Decimal` is implemented in software, so it will be slower than `double`, which is done by the FPU. However, `decimal` is more precise. — SLaks, Mar 04 '10 at 17:17
@Slaks - Thank you. I do know that. I was only trying to get Andrey's reasoning in case it was something else. I probably should have noted the trade off in my comment. — Mike Two, Mar 04 '10 at 17:20
You'll want to take a look at the index operator. See this question: http://stackoverflow.com/questions/424669/how-do-i-overload-the-operator-in-c — Stephen, Mar 04 '10 at 17:11

score 13 · Accepted Answer · answered Mar 04 '10 at 17:09

13

You need to write an indexer, like this:

public decimal this[int index] {
    get { return data[index]; }
    set { data[index] = value; }
}

answered Mar 04 '10 at 17:09

SLaks

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Thanks What I could not find documentation about what the indexer - just what I need – John Chenault Mar 04 '10 at 17:22
1

Then you should accept this answer by clicking the hollow check. – SLaks Mar 04 '10 at 17:28

Mike Two · Answer 2 · 2010-03-04T18:48:01.880

5

Use an indexer

public class MyValues {
    private readonly decimal[] numbers = new decimal[10];

    public decimal this[int index] {
        get { return numbers[index]; }
        set { numbers[index] = value; }
    }
}

You might want to add some bounds checking to provide better failiure messages. Also you probably do not want to hard code the array size.

edited Mar 04 '10 at 18:48

answered Mar 04 '10 at 17:10

Mike Two

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You don't need to add bounds checking - the array already does. – SLaks Mar 04 '10 at 17:27
@SLaks - yes of course, but you might want to fail in a different way than the way the array will fail. The "Clearly" part is clearly too strong here. – Mike Two Mar 04 '10 at 18:46

score 3 · Answer 3 · answered Mar 04 '10 at 17:14

Using an indexer, you could write a simple generic class like:

    public class FixedArray<T>
    {
        private T[] array;

        public int Length { get { return array.Length; } }

        public FixedArray (int size)
        {
            array = new T[size];
        }

        public T this[int index]
        {
            get { return array[index]; }
            set { array[index] = value; }
        }
    }

score 2 · Answer 4 · answered Mar 04 '10 at 17:10

2

something like:

decimal this[int ind]
{
   get
   {
      return array[ind];
   }
   set
   {
      array[ind] = value;
   }
}

answered Mar 04 '10 at 17:10

Andrey

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score 1 · Answer 5 · answered Mar 04 '10 at 17:09

1

Try ReadOnlyCollection class. Also be aware of the dangers of arrays, really good article here

answered Mar 04 '10 at 17:09

openshac

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Building an object with a [] interface ( not from ILIst) in c#

5 Answers5