Sort (Array array, System.Collections.IComparer? comparer) - parameter or implementation?-CodePudding

The Methode Array.Sort() has the following signature

public static void Sort (Array array, System.Collections.IComparer? comparer);

It looks like you need to pass an IComparer reference. But what is really needed is that array needs to implements IComparable, isn't it?

I see this syntax the first time. Is this common? How can I differentiate between a real parameter? Is there somewhere more information about this topic (in general)?

Important/Edit: ATM I'm reading a C# book and it says about Sort.Array (translated from German to English):

To the first parameter we pass the array to be sorted, in our case arr. The second parameter is of type IComparer interface. Of course, you can't pass an instance of type IComparer to the method call, because interfaces are not instantiable. This is not how the type specification of the second parameter should be understood. Instead, the second parameter simply requires that the fist argument passed to it be an object that implements the interface IComparer - whether the object is of type DemoClass, Circle,

Basically he says that the second parameter is kind of a description for the first parameter. Is he correct or maybe that's just wrong and the source for my confusion?

https://openbook.rheinwerk-verlag.de/visual_csharp_2012/1997_04_008.html

I just implemented the following snippet. So this could be a way how to pass the second parameter, right?

    Array.Sort(shapes, (a, b) => {
        if (a.GetArea() < b.GetArea()) return -1;
        else if (a.GetArea() > b.GetArea()) return 1;
        return 0;
    });

CodePudding user response：

If you do not pass the comparer it will use the default comparer implementation for the Array items. But if you have a special comparer then you can pass your own custom Comparer to sort the elements.

Suppose you have a Class of Students (Array of Students), and your default Student comparer can be based on total marks. However, a maths teacher may want to sort the Students based on marks for the Maths only, in that case maths teacher can write his custom MathsRankComparer and pass it to the Sort method so that he will get the Students ordered by marks in Maths.

Similarly, English or Science teacher can pass the respective comparers to get their required ranking/ordering/sorting.

Hope this helps in understanding use of that overload.

CodePudding user response：

I have seen IComparer a few times and am unsure what implements it as standard - as far as lists, arrays and things go. I do know that numbers implement it and I think string does too. You can though custom implement this inferface. If memory serves me correctly, it provides just one method (interface so you have to write logic yourself) that returns an int. -1 (<0) is lower ranked, 1(>0) is higher ranked, 0 is the same.