The Elegant Art of Programming

  1  /// <summary>
  2  /// Checks if all values are equal by means of the equality comparer.
  3  /// </summary>
  4  /// <typeparam name="TSource">The type of the elements of source.</typeparam>
  5  /// <param name="source">The sequence to check for all equal elements.</param>
  6  /// <returns>True if empty, has only one element, or all are equal; false otherwise.</returns>
  7  /// <exception cref="ArgumentNullException">source is null</exception>
  8  public static bool AllTheSame<TSource>(this IEnumerable<TSource> source)
  9  {
 10      return AllTheSame<TSource>(source, null);
 11  }
 12  /// <summary>
 13  /// Checks if all values are equal by means of the given comparer.
 14  /// </summary>
 15  /// <typeparam name="TSource">The type of the elements of source.</typeparam>
 16  /// <param name="source">The sequence to check for all equal elements.</param>
 17  /// <param name="comparer">An IEqualityComparer<TSource> to compare values.</param>
 18  /// <returns>True if empty, has only one element, or all are equal; false otherwise.</returns>
 19  /// <exception cref="ArgumentNullException">source is null</exception>
 20  public static bool AllTheSame<TSource>(this IEnumerable<TSource> source,
 21                                         IEqualityComparer<TSource> comparer)
 22  {
 23      // Check preconditions and do default handling.
 24      if (source == null) throw new ArgumentNullException("Value cannot be null.", "source");
 25      var equalityComparer = comparer ?? EqualityComparer<TSource>.Default;
 26              
 27      // Check if any element is different to the first one and return out of the loop if so.
 28      var it = source.GetEnumerator();
 29      if (it.MoveNext())
 30      {
 31          var first = it.Current;
 32          while (it.MoveNext()) if (!equalityComparer.Equals(first, it.Current)) return false;
 33      }
 34      return true;
 35  }

 27      ...
 28      var first = source.FirstOrDefault();
 29      foreach (var item in source) if (!equalityComparer.Equals(first, item)) return false;
 30      return true;
 31  }

 27      ...
 28      var first = source.FirstOrDefault();
 29      return source.All(e => equalityComparer.Equals(first, e));
 30  }