C# Enumerable DefaultIfEmpty(IEnumerable)

Description

Returns the elements of the specified sequence or the type parameter's default value in a singleton collection if the sequence is empty.

Syntax

public static IEnumerable<TSource> DefaultIfEmpty<TSource>(
  this IEnumerable<TSource> source
)

Parameters

• TSource - The type of the elements of source.
• source - The sequence to return a default value for if it is empty.

Returns

Returns the elements of the specified sequence or the type parameter's default value in a singleton collection if the sequence is empty.

Example

The following code examples demonstrate how to use DefaultIfEmpty(IEnumerable) to provide a default value in case the source sequence is empty.

//from   w  w  w.j a v  a 2  s.  c  o m
using System;
using System.Linq;
using System.Collections.Generic;
public class MainClass{
  public static void Main(String[] argv){  
      List<Pet> pets =
          new List<Pet>{ new Pet { Name="A", Age=8 },
                         new Pet { Name="B", Age=4 },
                         new Pet { Name="C", Age=1 } };

      foreach (Pet pet in pets.DefaultIfEmpty())
      {
          Console.WriteLine(pet.Name);
      }

  }
}
    
class Pet{
   public string Name { get; set; }
   public int Age { get; set; }
}

The code above generates the following result.