using System;

​

public class SubstringVsSpan

{

    public static void Main(string[] args)

    {

        string originalString = "This is a long string, with several: delimited: parts.";

​

        // --- Using Substring (creates new strings - allocations) ---

        Console.WriteLine("Using Substring:");

        SubstringExample(originalString);

​

        // --- Using ReadOnlySpan<char> (no allocations for slices) ---

        Console.WriteLine("\nUsing ReadOnlySpan<char>:");

        SpanExample(originalString);

    }

​

    static void SubstringExample(string text)

    {

        int startIndex = 0;

        int colonIndex;

​

        while ((colonIndex = text.IndexOf(':', startIndex)) != -1)

        {

            // Substring creates a NEW string object each time

            string part = text.Substring(startIndex, colonIndex - startIndex);

            ProcessStringPart(part);

            startIndex = colonIndex + 1;

        }

​

        // Process the last part (after the last colon)

        string lastPart = text.Substring(startIndex);

        ProcessStringPart(lastPart);

    }

​

    static void SpanExample(string text)

    {

        // Convert the string to a ReadOnlySpan<char> (no allocation here, just a view)

        ReadOnlySpan<char> textSpan = text.AsSpan();

​

        int startIndex = 0;

        int colonIndex;

​

        while ((colonIndex = textSpan.IndexOf(':')) != -1)

        {

            // Slice creates a new ReadOnlySpan<char> that refers to a portion

            // of the *original* string's memory.  NO new string is created.

            ReadOnlySpan<char> part = textSpan.Slice(startIndex, colonIndex - startIndex);

            ProcessSpanPart(part);

            //Important that we operate on the reduced slice, if we reuse textSpan we will loop forever

            textSpan = textSpan.Slice(colonIndex + 1);

            startIndex = 0; // Reset startIndex for the next slice

        }

​

        // Process the last part (after the last colon)

        ProcessSpanPart(textSpan); // textSpan already points to the last part

    }

​

​

​

    // Simulate processing a string part (using Substring)

    static void ProcessStringPart(string part)

    {

        Console.WriteLine($"  Processing string: '{part}'");  //Note, using the string here.

    }

​

    // Simulate processing a string part (using ReadOnlySpan<char>)

    static void ProcessSpanPart(ReadOnlySpan<char> part)

    {

        // Important: If you *need* a string, you can create one from the span,

        // but this *does* create a new string object. Avoid this if you can

        // work directly with the ReadOnlySpan<char>.

        //string partString = part.ToString(); // Allocation!

​

        // Often, you can work directly with the ReadOnlySpan<char> without

        // converting it to a string.  For example, you can compare it,

        // search within it, etc.

​

        Console.WriteLine($"  Processing span:   '{part.ToString()}'");  //For demo purposes converting.

​

        //Example of avoiding ToString() in a common case (comparison)

        if (part.SequenceEqual("delimited")) {

           Console.WriteLine("    Found the 'delimited' part!");

        }

    }

}