LINQ in Action Chapter 3

Short Description
This chapter covers:
+ An introduction to the key elements of the LINQ foundation
+ Sequences
+ Deferred query execution
+ Query operators
+ Query expressions
+ Expression trees
+ LINQ DLLs and namespaces

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Content
…An iterator is an object that allows you to traverse through a collection’s elements. What is named an iterator in .NET is also known as a generator in other languages such as Python, or sometimes a cursor, especially within the context of a database. You may not know what an iterator is, but you surely have used several of them before! Each time you use a foreach loop (For Each in VB.NET), an iterator is involved. (This isn’t true for arrays because the C# and VB.NET compilers optimize foreach and For Each loops over arrays to replace the use of iterators by a simple loop, as if a for loop were used.) Every .NET collection (List, Dictionary, and ArrayList for example) has a method named GetEnumerator that returns an object used to iterate over its contents. That’s what foreach uses behind the scenes to iterate on the items contained in a collection. If you’re interested in design patterns, you can study the classical Iterator pattern. This is the design iterators rely on in .NET.
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