The Tech Platform
Aug 18, 20212 min
The hat operator (^) and range operator (..) provide a different syntax for accessing elements in an array: Span, or ReadOnlySpan. The range operator is used to specify the start and end of a range for a sequence.
Let’s look at some examples. Consider the following code where you have an array of strings and you want to get the first four elements:
static void Main(string[] args)
{
var people = new string[] { "Jane", "Jean", "Grey", "Marcus", "Theophilus", "Keje" };
var firstFour = GetFirstFourPersons(people);
foreach (var person in firstFour)
{
Console.WriteLine(person);
}
}
static string[] GetFirstFourPersons(string[] people)
{
var result = new string[4];
for (int i = 0; i < 4; i++)
{
result[i] = people[i];
}
return result;
}
// result:
// Jane
// Jean
// Grey
// Marcus
We can rewrite it using the range operator, passing the range operand inside [ and ].
static void Main(string[] args)
{
var people = new string[] { "Jane", "Jean", "Grey", "Marcus", "Theophilus", "Keje" };
var firstFour = people[0..4];
foreach (var person in firstFour)
{
Console.WriteLine(person);
}
}
This gives the same result as the previous example. Before and after the .. operator are the start index and end index from which to get a sequence of data. It doesn't include the element in the end index as part of the result.
The range can also be open-ended. That means you can omit the start index, end index or both.
var all = people[..]; // contains all the elements from the origin array
var firstFour = people[..4]; // contains "Jane", "Jean", "Grey", and "Marcus"
var lastTwo = people[4..]; // contains "Theophilus" and "Keje"
The all variable is open-ended on both ends and therefore returns all the elements. It can also be written as var all = people[0..people.Length]. If you omit the start index, it'll use 0 as the start index, and if it's the end index, it'll use the value sequence.Length to resolve the value.
You can also declare range variables:
Range firstFourRange = ..4
var firstFour = people[firstFourRange]; // contains "Jane", "Jean", "Grey", and "Marcus"
With C# 8, you can specify that an index is relative to the end of the array. You do this using the ^ operator. Given the array people, we can get the last element in the sequence using people[^1]. The ^0 is the same as people.Length. So if you use people[^0] to get the last element of the sequence, you'll get an exception because it's outside the allowed range. We can use this with the range operator:
Range lastTwoElement = ^2..
var lastTwo = people[lastTwoElement] // contains "Theophilus" and "Keje"
This will give us the last two names. Omitting the end index translates to using ^0 (i.e. people.Length) as the end index. We can also assign the index to a variable:
Index lastIndex = ^1;
string value = people[lastIndex];
This language support is based on two new types, System.Index and System.Range. The Index type represents an index into a sequence, and the Range type specifies a sub-range of a sequence.
Source: Medium by MBARK T3STO
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