我已经实现了一个扩展方法包(在http://foop.codeplex.com/上可用)，其中一些是我日常使用的:

// the most beloved extension method for me is Pipe:
<%= variable.Pipe(x => this.SomeFunction(x)).Pipe(y =>
{
    ...;
    return this.SomeOtherFunction(y);
}) %>

var d = 28.December(2009); // some extension methods for creating DateTime
DateTime justDatePart = d.JustDate();
TimeSpan justTimePart = d.JustTime();
var nextTime = d.Add(5.Hours());

using(StreamReader reader = new StreamReader("lines-of-data-file-for-example")) {
    ...
    // for reading streams line by line and usable in LINQ
    var query = from line in reader.Lines(); 
                where line.Contains(_today)
                select new { Parts = PartsOf(line), Time = _now };
}

500.Sleep();

XmlSerialize and XmlDeserialize

IsNull and IsNotNull

IfTrue, IfFalse and Iff:
true.IfTrue(() => Console.WriteLine("it is true then!");

IfNull and IfNotNull

使用反射查找TryParse方法并在字符串目标上调用它。可选参数指定转换失败时应返回的内容。我发现这个方法在大多数时候都很有用。很清楚皈依者。ChangeType选项，但我发现这更有用的什么与默认结果方便和什么。请注意，找到的方法保存在字典中，尽管我确实怀疑装箱最终会降低一点速度。

这种方法是我最喜欢的，因为它合理地使用了许多语言特性。

private static readonly Dictionary<Type, MethodInfo> Parsers = new Dictionary<Type, MethodInfo>();

public static T Parse<T>(this string value, T defaultValue = default(T))
{
    if (string.IsNullOrEmpty(value)) return defaultValue;

    if (!Parsers.ContainsKey(typeof(T)))
        Parsers[typeof (T)] = typeof (T).GetMethods(BindingFlags.Public | BindingFlags.Static)
            .Where(mi => mi.Name == "TryParse")
            .Single(mi =>
                        {
                            var parameters = mi.GetParameters();
                            if (parameters.Length != 2) return false;
                            return parameters[0].ParameterType == typeof (string) &&
                                   parameters[1].ParameterType == typeof (T).MakeByRefType();
                        });

    var @params = new object[] {value, default(T)};
    return (bool) Parsers[typeof (T)].Invoke(null, @params) ?
        (T) @params[1] : defaultValue;
}

用法:

var hundredTwentyThree = "123".Parse(0);
var badnumber = "test".Parse(-1);
var date = "01/01/01".Parse<DateTime>();

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());
}

无论如何，把它放在codeplex项目中。

将对象序列化/反序列化为XML:

/// <summary>Serializes an object of type T in to an xml string</summary>
/// <typeparam name="T">Any class type</typeparam>
/// <param name="obj">Object to serialize</param>
/// <returns>A string that represents Xml, empty otherwise</returns>
public static string XmlSerialize<T>(this T obj) where T : class, new()
{
    if (obj == null) throw new ArgumentNullException("obj");

    var serializer = new XmlSerializer(typeof(T));
    using (var writer = new StringWriter())
    {
        serializer.Serialize(writer, obj);
        return writer.ToString();
    }
}

/// <summary>Deserializes an xml string in to an object of Type T</summary>
/// <typeparam name="T">Any class type</typeparam>
/// <param name="xml">Xml as string to deserialize from</param>
/// <returns>A new object of type T is successful, null if failed</returns>
public static T XmlDeserialize<T>(this string xml) where T : class, new()
{
    if (xml == null) throw new ArgumentNullException("xml");

    var serializer = new XmlSerializer(typeof(T));
    using (var reader = new StringReader(xml))
    {
        try { return (T)serializer.Deserialize(reader); }
        catch { return null; } // Could not be deserialized to this type.
    }
}

这是罗马数字的to-and-from。不常用，但可能很方便。用法:

if ("IV".IsValidRomanNumeral())
{
   // Do useful stuff with the number 4.
}

Console.WriteLine("MMMDCCCLXXXVIII".ParseRomanNumeral());
Console.WriteLine(3888.ToRomanNumeralString());

源:

    public static class RomanNumeralExtensions
    {
        private const int NumberOfRomanNumeralMaps = 13;

        private static readonly Dictionary<string, int> romanNumerals =
            new Dictionary<string, int>(NumberOfRomanNumeralMaps)
            {
                { "M", 1000 }, 
                { "CM", 900 }, 
                { "D", 500 }, 
                { "CD", 400 }, 
                { "C", 100 }, 
                { "XC", 90 }, 
                { "L", 50 }, 
                { "XL", 40 }, 
                { "X", 10 }, 
                { "IX", 9 }, 
                { "V", 5 }, 
                { "IV", 4 }, 
                { "I", 1 }
            };

        private static readonly Regex validRomanNumeral = new Regex(
            "^(?i:(?=[MDCLXVI])((M{0,3})((C[DM])|(D?C{0,3}))"
            + "?((X[LC])|(L?XX{0,2})|L)?((I[VX])|(V?(II{0,2}))|V)?))$", 
            RegexOptions.Compiled);

        public static bool IsValidRomanNumeral(this string value)
        {
            return validRomanNumeral.IsMatch(value);
        }

        public static int ParseRomanNumeral(this string value)
        {
            if (value == null)
            {
                throw new ArgumentNullException("value");
            }

            value = value.ToUpperInvariant().Trim();

            var length = value.Length;

            if ((length == 0) || !value.IsValidRomanNumeral())
            {
                throw new ArgumentException("Empty or invalid Roman numeral string.", "value");
            }

            var total = 0;
            var i = length;

            while (i > 0)
            {
                var digit = romanNumerals[value[--i].ToString()];

                if (i > 0)
                {
                    var previousDigit = romanNumerals[value[i - 1].ToString()];

                    if (previousDigit < digit)
                    {
                        digit -= previousDigit;
                        i--;
                    }
                }

                total += digit;
            }

            return total;
        }

        public static string ToRomanNumeralString(this int value)
        {
            const int MinValue = 1;
            const int MaxValue = 3999;

            if ((value < MinValue) || (value > MaxValue))
            {
                throw new ArgumentOutOfRangeException("value", value, "Argument out of Roman numeral range.");
            }

            const int MaxRomanNumeralLength = 15;
            var sb = new StringBuilder(MaxRomanNumeralLength);

            foreach (var pair in romanNumerals)
            {
                while (value / pair.Value > 0)
                {
                    sb.Append(pair.Key);
                    value -= pair.Value;
                }
            }

            return sb.ToString();
        }
    }

在这里找到更多的例子:www.extensionmethod.net