String slice

A string can be sliced. To do this, we provide a Slice() extension method. By slicing a string, we extract the characters from index one to index two.

Taking a slice is essentially the same as calling Substring with 2 index values. But sometimes using a second argument of the last index is easier.

Input and output

The key thing to remember with slice is that the second argument is an end index, not a length. And we can use a negative end index to count from the end.

Slice(1, 4)    ABCDEF
               BCD
Slice(3, -2)   The morning is upon us.
               morning is upon u

Example

Here we develop a method in C# to match JavaScript. With the JavaScript slice method, you pass it the start index, which must always be 0 or higher.

using System;

class Program
{
    static void Main()
    {
        Console.WriteLine("ABCDEF".Slice(1, 4));
        Console.WriteLine("The morning is upon us.".Slice(3, -2));

        string s = "0123456789_";
        // These slices are valid:
        Console.WriteLine(s.Slice(0, 1));  // First char
        Console.WriteLine(s.Slice(0, 2));  // First two chars
        Console.WriteLine(s.Slice(1, 2));  // Second char
        Console.WriteLine(s.Slice(8, 11)); // Last three chars
    }
}

public static class Extensions
{
    public static string Slice(this string source, int start, int end)
    {
        // Keep this for negative end support.
        if (end < 0) 
        {
            end = source.Length + end;
        }
        // Calculate length.
        int len = end - start;
        // Return Substring of length.
        return source.Substring(start, len);
    }
}
BCD
 morning is upon u
0
01
1
89_

Extension notes

This is an extension method. To create an extension method, use the this-keyword as the first parameter in a static method (in a static class).

Here we implemented a Slice() method. An extension method makes the syntax clearer—slice is useful enough to justify an extension method.