python字典方法:

/// <summary>
/// If a key exists in a dictionary, return its value, 
/// otherwise return the default value for that type.
/// </summary>
public static U GetWithDefault<T, U>(this Dictionary<T, U> dict, T key)
{
    return dict.GetWithDefault(key, default(U));
}

/// <summary>
/// If a key exists in a dictionary, return its value,
/// otherwise return the provided default value.
/// </summary>
public static U GetWithDefault<T, U>(this Dictionary<T, U> dict, T key, U defaultValue)
{
    return dict.ContainsKey(key)
        ? dict[key]
        : defaultValue;
}

当您希望将时间戳附加到文件名以确保唯一性时非常有用。

/// <summary>
/// Format a DateTime as a string that contains no characters
//// that are banned from filenames, such as ':'.
/// </summary>
/// <returns>YYYY-MM-DD_HH.MM.SS</returns>
public static string ToFilenameString(this DateTime dt)
{
    return dt.ToString("s").Replace(":", ".").Replace('T', '_');
}

我使用的两种颜色扩展，主要用于控件开发:

public static class ColorExtensions
{
  // Gets a color that will be readable on top of a given background color
  public static Color GetForegroundColor(this Color input)
  {
    // Math taken from one of the replies to
    // http://stackoverflow.com/questions/2241447/make-foregroundcolor-black-or-white-depending-on-background
    if (Math.Sqrt(input.R * input.R * .241 + input.G * input.G * .691 + input.B * input.B * .068) > 128)
      return Color.Black;
    else
      return Color.White;
  }

  // Converts a given Color to gray
  public static Color ToGray(this Color input)
  {
    int g = (int)(input.R * .299) + (int)(input.G * .587) + (int)(input.B * .114);
    return Color.FromArgb(input.A, g, g, g);
  }
}

用法:

Color foreColor = someBackColor.GetForegroundColor();
Color grayColor = someBackColor.ToGray();

简单但比“可枚举”更好。范围”,恕我直言:

/// <summary>
/// Replace "Enumerable.Range(n)" with "n.Range()":
/// </summary>
/// <param name="n">iterations</param>
/// <returns>0..n-1</returns>
public static IEnumerable<int> Range(this int n)
{
    for (int i = 0; i < n; i++)
        yield return i;
}

public static class EnumerableExtensions
{
    [Pure]
    public static U MapReduce<T, U>(this IEnumerable<T> enumerable, Func<T, U> map, Func<U, U, U> reduce)
    {
        CodeContract.RequiresAlways(enumerable != null);
        CodeContract.RequiresAlways(enumerable.Skip(1).Any());
        CodeContract.RequiresAlways(map != null);
        CodeContract.RequiresAlways(reduce != null);
        return enumerable.AsParallel().Select(map).Aggregate(reduce);
    }
    [Pure]
    public static U MapReduce<T, U>(this IList<T> list, Func<T, U> map, Func<U, U, U> reduce)
    {
        CodeContract.RequiresAlways(list != null);
        CodeContract.RequiresAlways(list.Count >= 2);
        CodeContract.RequiresAlways(map != null);
        CodeContract.RequiresAlways(reduce != null);
        U result = map(list[0]);
        for (int i = 1; i < list.Count; i++)
        {
            result = reduce(result,map(list[i]));
        }
        return result;
    }

    //Parallel version; creates garbage
    [Pure]
    public static U MapReduce<T, U>(this IList<T> list, Func<T, U> map, Func<U, U, U> reduce)
    {
        CodeContract.RequiresAlways(list != null);
        CodeContract.RequiresAlways(list.Skip(1).Any());
        CodeContract.RequiresAlways(map != null);
        CodeContract.RequiresAlways(reduce != null);

        U[] mapped = new U[list.Count];
        Parallel.For(0, mapped.Length, i =>
            {
                mapped[i] = map(list[i]);
            });
        U result = mapped[0];
        for (int i = 1; i < list.Count; i++)
        {
            result = reduce(result, mapped[i]);
        }
        return result;
    }

}

下面是我经常使用的演示格式。

public static string ToTitleCase(this string mText)
{
    if (mText == null) return mText;

    System.Globalization.CultureInfo cultureInfo = System.Threading.Thread.CurrentThread.CurrentCulture;
    System.Globalization.TextInfo textInfo = cultureInfo.TextInfo;

    // TextInfo.ToTitleCase only operates on the string if is all lower case, otherwise it returns the string unchanged.
    return textInfo.ToTitleCase(mText.ToLower());
}

ThrowIfArgumentIsNull是做空检查的好方法，我们都应该这样做。

public static class Extensions
{
    public static void ThrowIfArgumentIsNull<T>(this T obj, string parameterName) where T : class
    {
        if (obj == null) throw new ArgumentNullException(parameterName + " not allowed to be null");
    }
}

下面是使用它的方法，它适用于您的命名空间中的所有类或任何您使用该命名空间的地方。

internal class Test
{
    public Test(string input1)
    {
        input1.ThrowIfArgumentIsNull("input1");
    }
}

在CodePlex项目上使用这段代码是可以的。