Span<T>.Enumerator Struct in C#

Span<T> is a new feature introduced with C# 7.2 and supported in the .NET Core 2.1. It provides a type-safe access to a contiguous area of memory. This memory can be located on the heap, stack or formed a unallocated memory. Span<T> is defined as a ref struct, which means it is limited to being allocated only on the Stack. The main reason for the ref struct design is to ensure that when using of Span<T> it causes no additional heap allocations. Span<T> improves execution speed and reducing memory allocations in existing code.

Here, Span<T> references some contiguous memory(colored blocks) that has already been allocated.
Span<T>.Enumerator struct provides an enumerator for the elements of a Span<T>. Where Span<T> provides a type and memory safe representation of a contiguous region of arbitrary memory. 
Syntax:

public struct Span<T>.Enumerator

Parameter:
Here the parameter is T, where T is the type of items in the Span<T>.
Example:

csharp

// C# program to demonstrate Span<T>.Enumerator Struct
using System;
using System.Threading.Tasks;

class GFG {

    // a array "arr" type of byte
    private static byte[] arr = new byte[4];

    // main method
    static void Main()
    {
        // randomly fillup the array "arr"
        new Random(30).NextBytes(arr);

        // implicitly cast the array
        // "arr" to span<byte>
        Span<byte> sp = arr;

        // Task.Run() method executes
        // the clear() method
        // to clear the array for
        // each thread operations
        Task.Run(() => clear());

        // call the function "print"
        print(sp);

    }

    public static void clear()
    {
        // delay for 10ms
        Task.Delay(10).Wait();

        lock(arr)
        // defines that one thread
        // executes one task at one time
        {
            Array.Clear(arr, 0, arr.Length);
        }
    }

    // print function
    public static void print(Span<byte> span)
    {
        foreach(byte e in span)
        {
            Console.WriteLine(e);
            Task.Delay(10).Wait();
        }
    }
}

Output:

52
239
0
0

Properties:

• Current: It is used to get a reference to the item at the current position of the enumerator.

Methods: 

• MoveNext(): It advances the enumerator to the next item of the Span<T>.

Important Points:

• Span<T> provides a type-safe access to a contiguous area of memory.
• It cannot be used within asynchronous methods.
• It does not implement the IEnumerator or IEnumerator<T> interface, because Span<T> enumerator is a ref struct.
• It does not include a Reset method.
• For use the Reset() method, it must be implemented as part of the interface.
• It does not include additional heap allocation.
• It cannot be used as a generic type argument.
• Span<T> provides read-write access to the memory.
• ReadOnlySpan<T> provides read-only access to a memory.