C# in Depth

Introducing LINQ277the extension methods of Enumerable but do it without query expressions, does thatcount? What about plain lambda expressions without any querying going on?As a concrete example of this question, let’s consider four slightly different ways ofachieving the same goal. Suppose we have a List (where Person has propertiesName and Age as in chapter 8) and we wish to apply a transformation so that we geta sequence of strings, just the names of the people in the list. Using lambda expressionsin preference to anonymous methods, we can still use the standard ConvertAll methodof List, as follows:var names = people.ConvertAll(p => p.Name);Alternatively we can use the Select method of the Enumerable class, because Listimplements IEnumerable. The result of this will be an IEnumerablerather than a List, but in many cases that’s fine. The code becomesvar names = Enumerable.Select(people, p => p.Name);Knowing that Select is an extension method, we can simplify things a little bit:var names = people.Select(p => p.Name);Finally, we could use a query expression:var names = from p in people select p.Name;Four one-liners, all of which accomplish much the same goal. 2 Which of them count asLINQ? My personal answer is that the first isn’t really using LINQ (even though it uses alambda expression), but the rest are LINQ-based solutions. The second form certainlyisn’t idiomatic, but the last two are both perfectly respectable LINQ ways of achievingthe same aim, and in fact all of the last three samples compile to the same IL.In the end, there are no bonus points available for using LINQ, so the question ismoot. However, it’s worth being aware that when a fellow developer says they’re usingLINQ to solve a particular problem, that statement could have a variety of meanings.The long and the short of it is that LINQ is a collection of technologies, includingthe language features of C# 3 (and VB9) along with the framework libraries provided aspart of .NET 3.5. If your project targets .NET 3.5, you can use LINQ as much or as littleas you like. You can use just the support for in-memory querying, otherwise known asLINQ to Objects, or providers that target XML documents, relational databases, or otherdata sources. The only provider we’ll use in this chapter is LINQ to Objects, and in thenext chapter we’ll see how the same concepts apply to the other providers.There are a few concepts that are vital to LINQ. We’ve seen them tangentially inchapter 10, but let’s look at them a little more closely.11.1.2 Fundamental concepts in LINQMost of this chapter is dedicated to exactly what the C# 3 compiler does with queryexpressions, but it won’t make much sense until we have a better understanding of the2There’s actually a big difference between ConvertAll and Select, as we’ll see in a minute, but in many caseseither could be used.Licensed to Rhona Hadida