generic method not supporting constraints

Question

I am trying to write a generic method which should support intrinsic types for ex int, double, float etc. The method is sorting the array. I am getting a compile time error saying "cannot apply operator < to type T" which I understand, but how can I resolve it? Should I make the class generic and use constraints? Here is my code:

public static T[] Sort<T>(T[] inputArray) 
{
    for (int i = 1; i < inputArray.Length; i++)
    {
        for (int j = i - 1; j >= 0; j--)
        {
            ***if (inputArray[j + 1] < inputArray[j])***
            {
                T temp = inputArray[j + 1];
                inputArray[j + 1] = inputArray[j];
                inputArray[j] = temp;
            }
            else
            {
                break;
            }
        }
    }
    return inputArray;
}

Answer is you can't, there is very good post on SO about "generic operators constraint"... try searching - stackoverflow.com/search?q=[c%23]+generic+operator+constraint — Alexei Levenkov
– Alexei Levenkov, Commented Feb 6, 2014 at 17:57
There's stackoverflow.com/questions/2378466/… and stackoverflow.com/questions/390900/… — Preston Guillot
– Preston Guillot, Commented Feb 6, 2014 at 17:58

p.s.w.g · Accepted Answer · 2014-02-06 17:58:17Z

5

C# doesn't support generic constraints on what operators a type supports. However, .NET provides a number of interfaces that provide similar functionality. In this case, you need to add a generic constraint to ensure that T implements IComparable<T>.

public static T[] Sort<T>(T[] inputArray) where T : IComparable<T>
{
    for (int i = 1; i < inputArray.Length; i++)
    {
        for (int j = i - 1; j >= 0; j--)
        {
            if (inputArray[j + 1].CompareTo(inputArray[j]) < 0)
            {
                T temp = inputArray[j + 1];
                inputArray[j + 1] = inputArray[j];
                inputArray[j] = temp;
            }
            else
            {
                break;
            }
        }
    }
    return inputArray;
}

answered Feb 6, 2014 at 17:58

p.s.w.g

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Comments

Servy · Accepted Answer · 2014-02-06 17:57:48Z

3

There is no generic constraint that you can apply that will restrict types to those that have overloaded the < operator.

The best that you can do is restrict the type to those that implement IComparable<T> or accept a parameter of type IComparer<T> to do the comparisons (having two methods, one with each option, could also be worth doing).

answered Feb 6, 2014 at 17:57

Servy

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2 Comments

Haney Over a year ago

Good answer @Servy - this is basically why these interfaces exist.

Servy Over a year ago

@p.s.w.g Looks like there was some serial voting on my account. That should account for at least one, if not both of the DVs. We'll see whether both or just one goes away tonight.

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