extension-methods

I started with the IQueryable extension methods from this example on CodePlex . What i believe i need is an IQueryable extension method to "Where", where the method signature looks like: public static IQueryable<T> Where<T>(this IQueryable<T> source, string columnName, string keyword) and effectively does this (assuming T.columnName is of type string): source.Where(p => p.ColumnName.Contains("keyword")) using the above CodePlex example, i think i understand how he got the OrderBy method working, but my problem seems a bit more complex and I don't know how to get the Contains("keyword") part

So basically I wrote my little Add extension method for array types. using System; using System.Linq; public static class Extensions { public static void Add<T>(this T[] _self, T item) { _self = _self.Concat(new T[] { item }).ToArray(); } } public class Program { public static void Main() { string[] test = { "Hello" }; test = test.Concat(new string[] { "cruel" }).ToArray(); test.Add("but funny"); Console.WriteLine(String.Join(" ", test) + " world"); } } The output should be Hello cruel but funny world , but the but funny will never be concatenated within the extension method. Editing the same

My web application deals with strings that need to be converted to numbers a lot - users often put commas, units (like cm, m, g, kg) and currency symbols in these fields so what I want to do is create a string extension method that cleans the field up and converts it to a decimal. For example: decimal myNumber = "15 cm".ToDecimal(); Are you expecting users of different 'cultures' to use your application? If so it's better to factor in the user's regional settings: static decimal ToDecimal(this string str) { return Decimal.Parse(str, CultureInfo.CurrentCulture); } Or you could replace every

I was looking at this question and i was curious why this deosn't compile. Given this code, can anyone explain why the call to IBase.Test() doesn't resolve to the correct extension method? public interface IBase { } public interface IChildA : IBase { } public interface IChildB : IBase { } public static class BaseExtensions { public static IBase Test(this IBase self) { return self; } public static T Test<T>(this T self) where T : IChildB { return self; } } public static class TestClass { public static void Test() { IChildA a = null; //Yeh i know its null but just testing for compile here..

public abstract class Entity : IEntity { [Key] public virtual int Id { get; set; } } public class City:Entity { public string Code { get; set; } } public class BaseViewModel:IBaseViewModel { public int Id { get; set; } } public class CityModel:BaseViewModel { public string Code { get; set; } } my domain and view classes... and for mapping extension public static TModel ToModel<TModel,TEntity>(this TEntity entity) where TModel:IBaseViewModel where TEntity:IEntity { return Mapper.Map<TEntity, TModel>(entity); } and i am using like below City city = GetCity(Id); CityModel model = f.ToModel

Possible Duplicate: No type inference with generic extension method Consider two methods: public static IEnumerable<V> Merge<V> (this IEnumerable<IEnumerable<V>> coll) public static IEnumerable<V> Merge<T, V> (this IEnumerable<T> coll) where T : IEnumerable<V> Both compile just fine, in both cases the type of generic types will be known at compile time of caller, and thus the exact type of extended type. You can call both fine, but only the first one as extension. Why? Update 1 To see it fail, use the second method and such example: var x = new List<List<int>>(); var y = x.Merge(); Update --