Why StringBuilder class not having Contains method

Question

Dear Team,

In String Class, most "Contains" method is one of the most common methods, similarly, in StringBuilder class, I thought it should also have a similar method, but when I checked there was no such Method.

I knew, there may ways to encounter this problem like using our own extension method, or convert StringBuilder to String etc, but I want to know what is the reason behind not putting "Contains" method in StringBuilder class.

Thanks in Advance

Answer 1

Edit: missed the part about why there is no contains. IMHO it's because you can do contains, startswith, endswith etc against .ToString() which keeps StringBuilder focused on it's original intent to build efficient strings.

If we approach it from .ToString then we are dealing with a string.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using static System.Globalization.DateTimeFormatInfo;

namespace ConsoleNetCoreStringBuilder
{
    class Program
    {
        public static List<string> MonthNames() => 
            Enumerable.Range(1, 12).Select((index) => CurrentInfo.GetMonthName(index)).ToList();
        static void Main(string[] args)
        {
            StringBuilder builder = new ();

            MonthNames().ForEach(month => builder.AppendLine(month));

            Console.WriteLine(builder.ToString().Contains("April")); // yes
            Console.WriteLine(builder.ToString().Contains("april")); // no case sensitive
            Console.WriteLine(builder.ToString().Contains("april", StringComparison.OrdinalIgnoreCase)); // yes ignore case

            Console.ReadLine();
        }



    }


}

And then we can write an extension

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using static System.Globalization.DateTimeFormatInfo;

namespace ConsoleNetCoreStringBuilder
{
    class Program
    {
        public static List<string> MonthNames() => 
            Enumerable.Range(1, 12).Select((index) => CurrentInfo.GetMonthName(index)).ToList();
        static void Main(string[] args)
        {
            StringBuilder builder = new ();

            MonthNames().ForEach(month => builder.AppendLine(month));

            Console.WriteLine(builder.Contains("April")); // yes

            Console.ReadLine();
        }



    }

    public static class Extensions
    {
        public static bool Contains(this StringBuilder sender, string text) => 
            sender.ToString().Contains(text, StringComparison.OrdinalIgnoreCase);
    }


}

Answer 2

Hi @Tiwari, Nitendra

From the document below, which provide a sample how to achieve contain function.

public class StringBuilderFinder  
{  
   private StringBuilder sb;  
   private String text;  
     
   public StringBuilderFinder(StringBuilder sb, String textToFind)  
   {  
      this.sb = sb;  
      this.text = textToFind;  
   }  
     
   public bool SearchAndAppend(String stringToSearch)  
   {  
      sb.Append(stringToSearch);  
      return stringToSearch.Contains(text);  
   }  
}  

https://learn.microsoft.com/en-us/dotnet/api/system.text.stringbuilder?view=net-5.0#searching-the-text-in-a-stringbuilder-object

Best regards,
Zhanglong