Span

This is a generic C# type that can be used to act upon a region of memory. Span provides methods for testing, changing, and converting elements in memory.

Span usage

Span can be used with unsafe code for performance optimizations. It can also be used with arrays to perform low-level logic.

Fill

This program creates a Span of ints by passing an int array to the Span constructor. It then calls fill to change all elements to the value 5.

using System;

Span<int> span = new Span<int>(new int[] { 1, 2, 3 });
// Fill span with value 5.
span.Fill(5);
foreach (int value in span)
{
    Console.WriteLine(value);
}
5
5
5

ToArray

We can create a Span from a same-typed array. And in the same way, we can call ToArray to convert a span into an array of the same type.

using System;

var animals = new string[] { "bird", "frog", "dog" };
Span<string> span = new Span<string>(animals);

// Use ToArray to convert a span into an array.
string[] result = span.ToArray();
Console.WriteLine("RESULT: {0}", string.Join(",", result));
Console.WriteLine("RESULT LENGTH: {0}", result.Length);
RESULT: bird,frog,dog
RESULT LENGTH: 3

Slice

The Slice() method is like Substring for Spans—it receives a start index and an optional length as its arguments. It returns a new Span.

using System;

Span<int> span = new Span<int>(new int[] { 1, 2, 3 });

// Part 1: take slice at index 1 through the end.
var slice1 = span.Slice(1);
Console.WriteLine(string.Join(",", slice1.ToArray()));

// Part 2: take slice at index 0 with length 2.
var slice2 = span.Slice(0, 2);
Console.WriteLine(string.Join(",", slice2.ToArray()));
2,3
1,2

Pointer

We can create a Span from a pointer to memory in .NET Core. In this example, we use a fixed buffer as the pointer. We must specify the length of the span.

using System;

unsafe struct FixedBufferExample
{
    public fixed int _buffer[1024];
}

class Program
{
    static FixedBufferExample _fixedBufferExample;

    static void Main()
    {
        unsafe
        {
            // Part 1: store values in fixed buffer.
            fixed (int* buffer = _fixedBufferExample._buffer)
            {
                buffer[0] = 10;
                buffer[1] = 20;
                buffer[2] = 30;

                // Part 2: create span from fixed buffer struct.
                Span<int> span = new Span<int>(buffer, 3);
                foreach (int value in span)
                {
                    Console.WriteLine("BUFFER ELEMENT: {0}", value);
                }
            }
        }
    }
}
BUFFER ELEMENT: 10
BUFFER ELEMENT: 20
BUFFER ELEMENT: 30

Empty

To create an empty span, we can use the Span.Empty property. We must specify a type parameter on the Empty property. The resulting span has a length of 0.

using System;

Span<char> span = Span<char>.Empty;
Console.WriteLine("EMPTY LENGTH: {0}", span.Length);
EMPTY LENGTH: 0

ToString

Here we create a span of chars from a char array. We call ToCharArray to get a char array from a string. With a span, we can modify elements by assigning them.

using System;

Span<char> span = new Span<char>("bird".ToCharArray());
span[1] = 'a';
string result = span.ToString();
Console.WriteLine("RESULT: {0}", result);
RESULT: bard

Contains

Much like a string, we can use Contains to search a span. With a Span of chars, we can find a specific char—here we find the char "c" in the Span.

using System;

Span<char> span = new Span<char>(new char[] { 'a', 'b', 'c' });
// Use Contains to search a span.
if (span.Contains('c'))
{
    Console.WriteLine("SPAN CONTAINS C");
}
SPAN CONTAINS C

Span can receive an array, or a pointer to a region of memory. We can use string-like methods on Span like Contains or Slice. And we can loop with foreach over a Span.