extension-methods

I'm trying add the ability to lookup elements in a List<KeyValuePair<string,int>> by overriding the indexer. using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace ConsoleApplication2 { public class MyList : List<KeyValuePair<string, int>> { public int this[string key] { get { return base.Single(item => item.Key == key).Value; } } } } For some reason, the compiler is throwing this error: ' System.Collections.Generic.List<System.Collections.Generic.KeyValuePair<string,int>> ' does not contain a definition for ' Single '.

I really like Last() and would use it all the time for List<T> s. But since it seems to be defined for IEnumerable<T> , I guess it enumerates the enumeration first - this should be O(n) as opposed to O(1) for directly indexing the last element of a List<T> . Are the standard (Linq) extension methods aware of this? The STL in C++ is aware of this by virtue of a whole "inheritance tree" for iterators and whatnot. Martin Harris I just used the Reference Source to look into the code for Last and it checks to see if it is a IList<T> first and performs the appropriate O(1) call: public static

I want to be able to write extension methods so that I can say: lines.ForceSpaceGroupsToBeTabs(); instead of: lines = lines.ForceSpaceGroupsToBeTabs(); However, the following code currently outputs: ....one ........two instead of: Tone TTtwo What do I have to change in the following code to make it output: Tone TTtwo (note that for visibility, . = space, T = \t ): using System; using System.Collections.Generic; namespace TestExtended82343 { class Program { static void Main(string[] args) { List<string> lines = new List<string>(); lines.Add("....one"); lines.Add("........two"); lines

I want to do this, but getting this error: Error 1 Cannot define a new extension method because the compiler required type 'System.Runtime.CompilerServices.ExtensionAttribute' cannot be found. Are you missing a reference to System.Core.dll? [snipped some path stuff] I have seen some answers here that says, you have to define this attribute yourself. How do I do that? EDIT : This is what I have: [AttributeUsage ( AttributeTargets.Assembly | AttributeTargets.Class | AttributeTargets.Method )] public sealed class ExtensionAttribute : Attribute { public static int MeasureDisplayStringWidth ( this

I am trying to implement an outer join on this kind of query for the p.Person table. How would I do this? This example is taken from http://ashishware.com/DSLinqExample.shtml var onlyinfo = p.Person .Where(n => n.FirstName.Contains('a')) .Join(p.PersonInfo, n => n.PersonId, m => m.PersonId, (n, m) => m) .ToArray<Persons.PersonInfoRow>(); Jon Skeet Normally left joins in LINQ are modelled with group joins, sometimes in conjunction with DefaultIfEmpty and SelectMany : var leftJoin = p.Person.Where(n => n.FirstName.Contains("a")) .GroupJoin(p.PersonInfo, n => n.PersonId, m => m.PersonId, (n, ms)