Dr. Dobb's Journal - February 2008 - (Page 58)

d02hoff_p4ma 12/7/07 1:44 PM Page 58 Core Technology CONTINUOUS LINQ Listing One public static class ContinuousQueryExtension { #region Where public static ContinuousCollection%T> Where%T>( this ContinuousCollection%T> source, Func%T, bool> filterFunc) where T: IEquatable%T> { Trace.WriteLine("Filtering Observable Collection."); ContinuousCollection%T> output = new ContinuousCollection%T>(); FilteringViewAdapter%T> fva = new FilteringViewAdapter%T>(source, output, filterFunc); return output; } #endregion #region OrderBy public static ContinuousCollection%TSource> OrderBy%TSource, TKey>( this ContinuousCollection%TSource> source, Func%TSource, TKey> keySelector) where TSource : IEquatable%TSource> where TKey : IComparable { Trace.WriteLine("Ordering Observable Collection (Ascending)."); ContinuousCollection%TSource> output = new ContinuousCollection%TSource>(); SortingViewAdapter%TSource, TKey> sva = new SortingViewAdapter%TSource, TKey>( source, output, new FuncComparer%TSource, TKey>(keySelector, false)); return output; } #endregion #region OrderByDescending public static ContinuousCollection%TSource> OrderByDescending%TSource, TKey>( this ContinuousCollection%TSource> source, Func%TSource, TKey> keySelector) where TSource : IEquatable%TSource> where TKey : IComparable { Trace.WriteLine("Ordering Observable Collection (Descending)."); ContinuousCollection%TSource> output = new ContinuousCollection%TSource>(); SortingViewAdapter%TSource, TKey> sva = new SortingViewAdapter%TSource, TKey>( source, output, new FuncComparer%TSource, TKey>(keySelector, true)); return output; } #endregion } comes in, the query results are not affected. If a new tick comes in for AAPL, it is placed in the appropriate listbox based on the side of the tick. All of that work, decision making, and data propagation is done automatically by the CLINQ language extension. Fortunately, language extensions and CLINQ specifically can be used for pleasure as well as business. The following query is one that might be used in a strategy game to detect all nearby ships within your particular radar range: _visibleObjects = from radarObject in _rawRadar where radarObject .Distance2DFrom(_myLocation) <= RADAR_RADIUS select radarObject; Listing Two public void SubscribeToSymbol(MarketSymbol symbol) { if (!ModelRoot.Current.SubscribedSymbols.Contains(symbol)) { ModelRoot.Current.SubscribedSymbols.Add(symbol); MarketDataBook newBook = new MarketDataBook(); // WPF Window newBook.Symbol = symbol; newBook.AskTicks = from tick in ModelRoot.Current.MarketData where tick.Side == TickSide.Ask && tick.Symbol == symbol orderby tick.Price descending select tick; // SELL newBook.BidTicks = from tick in ModelRoot.Current.MarketData where tick.Side == TickSide.Bid && tick.Symbol == symbol orderby tick.Price select tick; // BUY _monitorBooks.Add(symbol, newBook); } } Such a game could receive a continuous stream of network messages from connected peer applications and store those messages in a ContinuousCollection (such as _rawRadar). The collection _visibleObjects would automatically update everytime an object in the _rawRadar list changed position or objects were added or removed. 58 Figure 3 shows the results of that query bound to a custom-style listbox to create a WPF-based radar view of nearby enemies. Conclusion Continuous LINQ is just one expansion made possible through language extensions and LINQ on the .NET Framework 3.5. By embracing these features of the upcoming version of .NET, you can be ready to not only provide the most advanced features in your applications, but you can be assured that if there are domain-specific query features that you want in your application, you can create them yourself quickly and easily. You can download the samples used in this article, as well as the CLINQ code itself, from my blog at dotnetaddict .dotnetdevelopersjournal.com. DDJ Dr. Dobb’s Journal l www.ddj.com l February 2008 http://dotnetaddict.dotnetdevelopersjournal.com http://dotnetaddict.dotnetdevelopersjournal.com http://www.ddj.com

Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - February 2008

Dr. Dobb's Journal - February 2008 Contents Hmmmm Alia Vox Developer Diaries Developer’s Notebook South American Software Development Conversations Inside Visual Studio 2008 BibPort: Creating Bibliographic References Continuous LINQ The ZK Framework Static Testing C++ Code The Agile Edge Effective Concurrency Swaine’s Flames

Dr. Dobb's Journal - February 2008

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