What is the difference between the ranges "^4" and "^4.."?-CodePudding

I was trying to get the substring from a string I am using in my program as follows:

mystring.Substring(mystring.Length - 4)

The Visual Studio IntelliSense recommended I use index and range operators as follows:

mystring[^4..]

I glanced through the documentation here and it seems like using just mystring[^4] would work just fine. Why does the IntelliSense recommend to use the extra .. in there, are there any benefits from adding it?

CodePudding user response：

^4 is an index, representing a single index number which just so happens to be 4 away from the end of the array. This is essentially the same as doing mystring[0], just dynamically figuring out the number based on the length.

^4.. is a range, which means everything between (and including) the 4th-to-last index and the end of the array.

var input = "abcdefghijk";
Console.WriteLine(input[^4]);
Console.WriteLine(input[^4..]);

This prints

h
hijk

CodePudding user response：

The .. operator is used to specify a range, while the values on either side are used to indicate indexes.

Using a single index will give a single value, using the .. operator will give a slice of multiple values:

public static void Main()
    {
        var array = new int[] { 1, 2, 3, 4, 5 };

        Console.WriteLine(array[^3].GetType());
        // Equivalent to 
        // array[new Index(3, fromEnd: true)]

        Console.WriteLine(array[^3..].GetType());
        // Equivalent to 
        // array[Range.EndAt(new Index(3, fromEnd: true))]
    }

Outputs

System.Int32 // notice the lack of []
System.Int32[]