Factory Pattern

Overview

• Factory Pattern is a creational design pattern that provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created.

Use Case

• When you want to create objects without exposing the creation logic to the client and refer to the newly created object using a common interface.

Code

• Suppose we're writing a report exporter.

   public interface IExporter
   {
       void Export(string data);
   }
  
   public class PdfExporter :IExporter
   {
       public void Export(string data)
       {
           Console.WriteLine("Exporting data to PDF: " + data);
       }
   }
   public class CsvExporter : IExporter
   {
       public void Export(string data)
       {
           Console.WriteLine("Exporting data to CSV: " + data);
       }
   }
   public class ExcelExporter : IExporter
   {
       public void Export(string data)
       {
           Console.WriteLine("Exporting data to Excel: " + data);
       }
   }
  

• Then our main method look like this

  private static void Main()
  {
      // This could be dynamically set based on user input or configuration
      string format = "pdf"; 
      IExporter exporter;
  
      if (format == "pdf")
      {
          exporter = new PdfExporter();
      }
      else if (format == "csv")
      {
          exporter = new CsvExporter();
      }
      else if (format == "excel")
      {
          exporter = new ExcelExporter();
      }
      else
      {
          throw new ArgumentException("Invalid export format");
      }
      exporter.Export("Sample Data");
  }
  

• Using factory pattern, we can refactor the code to remove the conditional logic to factory class

 public class ExporterFactory
 {
     public static IExporter GetExporter(string format)
     {
         return format.ToLower() switch
         {
             "pdf" => new PdfExporter(),
             "csv" => new CsvExporter(),
             "excel" => new ExcelExporter(),
             _ => throw new ArgumentException("Invalid export format")
         };
     }
 }
 ```

 - So now our main method can be simplified to:
```csharp
private static void Main()
{
    // This could be dynamically set based on user input or configuration
    string format = "pdf"; 
    IExporter exporter = ExporterFactory.GetExporter(format);
    exporter.Export("Sample Data");
}