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  • How To? Use an Expression Tree to call a Generic Method when the Type is only known at runtime.

    - by David Williams
    Please bear with me; I am very new to expression trees and lambda expressions, but trying to learn. This is something that I solved using reflection, but would like to see how to do it using expression trees. I have a generic function: private void DoSomeThing<T>( param object[] args ) { // Some work is done here. } that I need to call from else where in my class. Now, normally, this would be be simple: DoSomeThing<int>( blah ); but only if I know, at design time that I am working with an int. When I do not know the type until runtime is where I need the help. Like I said, I know how to do it via reflection, but I would like to do it via expression trees, as my (very limited) understanding is that I can do so. Any suggestions or points to sites where I can get this understanding, preferably with sample code?

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  • How to create a dynamic Linq Join extension method

    - by Royd Brayshay
    There was a library of dynamic Linq extensions methods released as a sample with VS2008. I'd like to extend it with a Join method. The code below fails with a parameter miss match exception at run time. Can anyone find the problem? public static IQueryable Join(this IQueryable outer, IEnumerable inner, string outerSelector, string innerSelector, string resultsSelector, params object[] values) { if (inner == null) throw new ArgumentNullException("inner"); if (outerSelector == null) throw new ArgumentNullException("outerSelector"); if (innerSelector == null) throw new ArgumentNullException("innerSelector"); if (resultsSelector == null) throw new ArgumentNullException("resultsSelctor"); LambdaExpression outerSelectorLambda = DynamicExpression.ParseLambda(outer.ElementType, null, outerSelector, values); LambdaExpression innerSelectorLambda = DynamicExpression.ParseLambda(inner.AsQueryable().ElementType, null, innerSelector, values); ParameterExpression[] parameters = new ParameterExpression[] { Expression.Parameter(outer.ElementType, "outer"), Expression.Parameter(inner.AsQueryable().ElementType, "inner") }; LambdaExpression resultsSelectorLambda = DynamicExpression.ParseLambda(parameters, null, resultsSelector, values); return outer.Provider.CreateQuery( Expression.Call( typeof(Queryable), "Join", new Type[] { outer.ElementType, inner.AsQueryable().ElementType, outerSelectorLambda.Body.Type, innerSelectorLambda.Body.Type, resultsSelectorLambda.Body.Type }, outer.Expression, inner.AsQueryable().Expression, Expression.Quote(outerSelectorLambda), Expression.Quote(innerSelectorLambda), Expression.Quote(resultsSelectorLambda))); } I've now fixed it myself, here's the answer. Please vote it up or add a better one.

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  • Compilation error while compiling an existing code base

    - by brijesh
    Hi, While building an existing code base on Mac OS using its native build setup I am getting some basic strange error while compilation phase. /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/bits/locale_facets.h: In constructor 'std::collate_byname<_CharT::collate_byname(const char*, size_t)': /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/bits/locale_facets.h:1072: error: '_M_c_locale_collate' was not declared in this scope /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/ppc-darwin/bits/messages_members.h: In constructor 'std::messages_byname<_CharT::messages_byname(const char*, size_t)': /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/ppc-darwin/bits/messages_members.h:79: error: '_M_c_locale_messages' was not declared in this scope /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits: At global scope: /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:897: error: 'float __builtin_huge_valf()' cannot appear in a constant-expression /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:897: error: a function call cannot appear in a constant-expression /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:897: error: 'float __builtin_huge_valf()' cannot appear in a constant-expression /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:897: error: a function call cannot appear in a constant-expression /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:899: error: 'float __builtin_nanf(const char*)' cannot appear in a constant-expression /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:899: error: a function call cannot appear in a constant-expression /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:899: error: 'float __builtin_nanf(const char*)' cannot appear in a constant-expression /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:899: error: a function call cannot appear in a constant-expression /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:900: error: field initializer is not constant /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:915: error: field initializer is not constant

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  • Passing in a lambda to a Where statement

    - by sonicblis
    I noticed today that if I do this: var items = context.items.Where(i => i.Property < 2); items = items.Where(i => i.Property > 4); Once I access the items var, it executes only the first line as the data call and then does the second call in memory. However, if I do this: var items = context.items.Where(i => i.Property < 2).Where(i => i.Property > 4); I get only one expression executed against the context that includes both where statements. I have a host of variables that I want to use to build the expression for the linq lambda, but their presence or absence changes the expression such that I'd have to have a rediculous number of conditionals to satisfy all cases. I thought I could just add the Where() statements as in my first example above, but that doesn't end up in a single expression that contains all of the criteria. Therefore, I'm trying to create just the lambda itself as such: //bogus syntax if (var1 == "something") var expression = Expression<Func<item, bool>>(i => i.Property == "Something); if (var2 == "somethingElse") expression = expression.Where(i => i.Property2 == "SomethingElse"); And then pass that in to the where of my context.Items to evaluate. A) is this right, and B) if so, how do you do it?

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  • Creating a sort function for a generic list

    - by Andrey
    I have a method for sorting generic lists by the object fields: public static IQueryable<T> SortTable<T>(IQueryable<T> q, string sortfield, bool ascending) { var p = Expression.Parameter(typeof(T), "p"); if (typeof(T).GetProperty(sortfield).PropertyType == typeof(int?)) { var x = Expression.Lambda<Func<T, int?>>(Expression.Property(p, sortfield), p); if (ascending) q = q.OrderBy(x); else q = q.OrderByDescending(x); } else if (typeof(T).GetProperty(sortfield).PropertyType == typeof(int)) { var x = Expression.Lambda<Func<T, int>>(Expression.Property(p, sortfield), p); if (ascending) q = q.OrderBy(x); else q = q.OrderByDescending(x); } else if (typeof(T).GetProperty(sortfield).PropertyType == typeof(DateTime)) { var x = Expression.Lambda<Func<T, DateTime>>(Expression.Property(p, sortfield), p); if (ascending) q = q.OrderBy(x); else q = q.OrderByDescending(x); } // many more for every type return q; } Is there any way I can collapse those ifs to a single generic statement? The main problem is that for the part Expression.Lambda<Func<T, int>> I am not sure how to write it generically.

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  • Linking LLVM JIT Code to Static LLVM Libraries?

    - by inflector
    I'm in the process of implementing a cross-platform (Mac OS X, Windows, and Linux) application which will do lots of CPU intensive analysis of financial data. The bulk of the analysis engine will be written in C++ for speed reasons, with a user-accessible scripting engine interfacing with the C++ testing engine. I want to write several scripting front-ends over time to emulate other popular software with existing large user bases. The first front will be a VisualBasic-like scripting language. I'm thinking that LLVM would be perfect for my needs. Performance is very important because of the sheer amount of data; it can take hours or days to run a single run of tests to get an answer. I believe that using LLVM will also allow me to use a single back-end solution while I implement different front-ends for different flavors of the scripting language over time. The testing engine itself will be separated from the interface and testing will even take place in a separate process with progress and results being reported to the testing management interface. Tests will consist of scripting code integrated with the testing engine code. In a previous implementation of a similar commercial testing system I wrote, I built a fast interpreter which easily interfaced with the testing library because it was written in C++ and linked directly to the testing engine library. Callbacks from scripting code to testing library objects involved translating between the formats with significant overhead. I'm imagining that with LLVM, I could implement the callbacks into C++ directly so that I could make the scripting code work almost as if it had been written in C++. Likewise, if all the code was compiled to LLVM byte-code format, it seems like the LLVM optimizers could optimize across the boundaries between the scripting language and the testing engine code that was written in C++. I don't want to have to compile the testing engine every time. Ideally, I'd like to JIT compile only the scripting code. For small tests, I'd skip some optimization passes, while for large tests, I'd perform full optimizations during the link. So is this possible? Can I precompile the testing engine to a .o object file or .a library file and then link in the scripting code using the JIT? Finally, ideally, I'd like to have the scripting code implement specific methods as subclasses for a specific C++ class. So the C++ testing engine would only see C++ objects while the JIT setup code compiled scripting code that implemented some of the methods for the objects. It seems that if I used the right name mangling algorithm it would be relatively easy to set up the LLVM generation for the scripting language to look like a C++ method call which could then be linked into the testing engine. Thus the linking stage would go in two directions, calls from the scripting language into the testing engine objects to retrieve pricing information and test state information and calls from the testing engine of methods of some particular C++ objects where the code was supplied not from C++ but from the scripting language. In summary: 1) Can I link in precompiled (either .bc, .o, or .a) files as part of the JIT compilation, code-generation process? 2) Can I link in code using that the process in 1) above in such a way that I am able to create code that acts as if it was all written in C++?

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  • Blog Engine .NET with XML Data Storage How is it so fast ?

    - by Kubi
    I am looking for a way to embed a blog engine into my own application and I am too curious about Blog Engine algorithm. This may not be the correct place to ask but, How is that possible to store blog entry data in an XML file like BlogEngine.Net with Default Configuration. It must be getting slower everyday while the file is getting larger and larger. I am wondering the algorithm behind that. Is it loading with a different way ? Or Am I wrong with the time estimation ? I know it is open source but I thought it would be better to see a discussion here for some others might be thinking the same and this thread can be a reference.

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  • Which is a better option, OpenGL or a game engine for developing a game for the iphone or ipod touch

    - by balraj
    I am new to OpenGL ES, and I'm about to begin a 3D game for the iphone in which we are showing some car pursuit or racing. Is it possible just with the OpenGL ES or UIKit only, or do I have to use other tools for it? I am comfortable with UIKit but newer to OpenGL/OpenGL ES; which would be better to start this game? Or should I use a game engine? If so, then which game engine would give us the 3D feeling, quality of images and motion, and rendering of the views with the sound effects?

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  • Flex: Would a computational engine for a Connect-4 type game be too slow?

    - by Robusto
    OK, I was just fooling around in my spare time and have made this cool interface and game-playing code for a Connect-4 type game, written in Flex and playable by 2 human players in Flash. It accurately detects wins, etc. I'm smart enough to know that I've done the easy part. Before I dig into an AI for game play, I wanted to ask if this is the kind of thing that can really be handled computationally by a Flash plugin. It seems to me that for every turn up until the end there are 8 possible moves, 8 responses to each move, etc. So wouldn't a perfect engine have to be able to potentially see 8^8 moves (over 16 million), and a fairly good engine see up to a million? I don't know game coding so this is new to me. What's a reasonable move horizon for such a game to be able to see?

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  • Configuring a html page from an original demo page

    - by Wold
    I forked into rainyday.js through github, an awesome javascript program made by maroslaw at this link: https://github.com/maroslaw/rainyday.js. Basically I tried taking his demo page and my own photo city.jpg and changed the applicable fields so that I could run it on my own site, but only the picture loads and the script itself doesn't start to run. I'm pretty new to html and javascript so I'm probably omitting something very simple, but here is the script for the demo code: <script src="rainyday.js"></script> <script> function getURLParameter(name) { return decodeURIComponent((new RegExp('[?|&]' + name + '=' + '([^&;]+?)(&|#|;|$)').exec(location.search)||[,''])[1].replace(/\+/g, '%20'))||null; } function demo() { var image = document.getElementById('background'); image.onload = function () { var engine = null; var preset = getURLParameter('preset') || '1'; if (preset === '1') { engine = new RainyDay({ element: 'background', blur: 10, opacity: 1, fps: 30, speed: 30 }); engine.rain([ [1, 2, 8000] ]); engine.rain([ [3, 3, 0.88], [5, 5, 0.9], [6, 2, 1] ], 100); } else if (preset === '2') { engine = new RainyDay({ element: 'background', blur: 10, opacity: 1, fps: 30, speed: 30 }); engine.VARIABLE_GRAVITY_ANGLE = Math.PI / 8; engine.rain([ [0, 2, 0.5], [4, 4, 1] ], 50); } else if (preset === '3') { engine = new RainyDay({ element: 'background', blur: 10, opacity: 1, fps: 30, speed: 30 }); engine.trail = engine.TRAIL_SMUDGE; engine.rain([ [0, 2, 0.5], [4, 4, 1] ], 100); } }; image.crossOrigin = 'anonymous'; if (getURLParameter('imgur')) { image.src = 'http://i.imgur.com/' + getURLParameter('imgur') + '.jpg'; } else if (getURLParameter('img')) { image.src = getURLParameter('img') + '.jpg'; } var youtube = getURLParameter('youtube'); if (youtube) { var div = document.getElementById('sound'); var player = document.createElement('iframe'); player.frameborder = '0'; player.height = '1'; player.width = '1'; player.src = 'https://youtube.com/embed/' + youtube + '?autoplay=1&controls=0&showinfo=0&autohide=1&loop=1'; div.appendChild(player); } } </script> This is where I am naming my background and specifying the photo from within the directory. <body onload="demo();"> <div id="sound" style="z-index: -1;"></div> <div id="parent"> <img id='background' alt="background" src="city.jpg" /> </div> </body> The actual code for the whole entire rainyday.js script can be found here: https://github.com/maroslaw/rainyday.js/blob/master/rainyday.js Thanks in advance for any help and advice!

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  • Where in the user profile are the Firefox search engine choices stored?

    - by N Rahl
    We have a large number of user profiles that were created on Ubuntu 10.04 and they had access to Google as a choice in the search bar and Google was the provider for queries typed into the super bar. When logging into these same profiles from Mint 15 client machines, the Google search option does not exist for these users, as is the default for Mint. This setting seems to be user specific, but not a part of the FireFox profile? It seems if it were a part of the FF profile, it would "just work" on Mint for these profiles, so I suspect the configuration may be stored somewhere else in the user's profile? Could someone please tell me where in a user's profile the search engine options are set? We would like to set this once, and then drop this configuration into everyones profile so all of our users don't have to do this manually.

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  • Is there any descent open-source search engine solutions?

    - by Nazariy
    Few weeks ago my friend asked me how hard is it to launch your own search engine service with list of websites that suppose to be crawled time to time. First what come at my mind was Google Custom Search however pricing policy is quite tricky and would drain your budget if you reach 500K queries per year. Another solution I found here was SearchBlox, which can be compared to Google Mini service. It's quite good solution if you planing to cover search over small amount of websites but for larger projects it is not very handy. I also found few other search platforms like Lucene, Hadoop and Xapian which seems to be quite powerful solutions to reach Google search quality, and Nutch as a web crawler. As most of open-source projects they share same problem, luck of comprehensive guidance of usage, examples and it's expected that you are expert in this subject. I'm wondering if any of you using this solutions, which of them would you recommend, and what should I be aware of?

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  • Getting chrome to distinguish between search engine query or URL entry?

    - by RoboShop
    So I use the quick search engine thing on chrome a lot. I type "w superman" if I want to find the wikipedia article for superman and even "tfs 13323" if I want to find the work item in TFS. The only problem is that with Google's new auto complete thing, sometimes I'll type in tfs 13030 and I'll get taken to the google search page having searched for "tfs 13030". The only way I can get rid of this is to clear my browser history. I guess the problem with using search and url on both the same bar is it gets confused about whether ur searching or ur entering a url. Is there a way around this?

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  • Backup and restore Subversion user permissions

    - by Earth Engine
    We use svnsync to create fully functional backup servers, and we have a script to do so. However if we wanted to create a new backup server, we have to copy the htpasswd and groups.conf file across (that is not hard) and (after running svnsync) manually assign the user/group to repositories. Also, if we change the assignment in the main server, there is no easy way to apply that change to all backup servers. Since we have 50+ projects and 30+ users this is a boring and error-pond exercise. Are there any tools that can help us to backup and restore those automatically? We are using VisualSVN under Windows, so it is better to have solutions in Windows scripts, not shell scripts.

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  • How to modify the language used by the Google Search Engine on IE 9.0?

    - by Seb Killer
    I would like to know how we can modify the settings of the Google Search Engine used in Internet Explorer 9.0 to force to use a specific language. Our problem is the following: as it uses geolocation by default, and we are in Switzerland, it takes the first of the official languages this is Swiss-German. However, we are located in Geneva where French is the official language. Furthermore, as most of our users speak English, we would like to force the language to be English and not Swiss-German. Does anybody know how to achieve this ? Thanks alot, Sébastien

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  • How to convert int to char in JSP expression language?

    - by james.bunt
    I need to display incremented single characters to denote footnotes in a table of data in a JSP. In Java I would normally have a char variable and just increment it, or convert an int to a char by casting it (e.g. (char)(i + 97) to convert a 0-based index to a-z). I can't figure out how to do this in expression language short of writing my own JSTL function. Does anyone know how to convert an int to char in EL? Or how to increment a char variable in EL? Or possibly even a better technique to do what I'm trying to do in JSP/EL? Example of what I need to be able to produce: a mydata b myotherdata ... a first footnote b second footnote

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  • java.sql.Exception ClosedConnection

    - by john
    I am getting the following error: java.sql.SQLException: Closed Connection at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:112) at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:146) at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:208) at oracle.jdbc.driver.PhysicalConnection.getMetaData(PhysicalConnection.java:1508) at com.ibatis.sqlmap.engine.execution.SqlExecutor.moveToNextResultsSafely(SqlExecutor.java:348) at com.ibatis.sqlmap.engine.execution.SqlExecutor.handleMultipleResults(SqlExecutor.java:320) at com.ibatis.sqlmap.engine.execution.SqlExecutor.executeQueryProcedure(SqlExecutor.java:277) at com.ibatis.sqlmap.engine.mapping.statement.ProcedureStatement.sqlExecuteQuery(ProcedureStatement.java:34) at com.ibatis.sqlmap.engine.mapping.statement.GeneralStatement.executeQueryWithCallback(GeneralStatement.java:173) at com.ibatis.sqlmap.engine.mapping.statement.GeneralStatement.executeQueryForList(GeneralStatement.java:123) at com.ibatis.sqlmap.engine.impl.SqlMapExecutorDelegate.queryForList(SqlMapExecutorDelegate.java:614) at com.ibatis.sqlmap.engine.impl.SqlMapExecutorDelegate.queryForList(SqlMapExecutorDelegate.java:588) at com.ibatis.sqlmap.engine.impl.SqlMapSessionImpl.queryForList(SqlMapSessionImpl.java:118) at org.springframework.orm.ibatis.SqlMapClientTemplate$3.doInSqlMapClient(SqlMapClientTemplate.java:268) at org.springframework.orm.ibatis.SqlMapClientTemplate.execute(SqlMapClientTemplate.java:193) at org.springframework.orm.ibatis.SqlMapClientTemplate.executeWithListResult(SqlMapClientTemplate.java:219) at org.springframework.orm.ibatis.SqlMapClientTemplate.queryForList(SqlMapClientTemplate.java:266) at gov.hud.pih.eiv.web.authentication.AuthenticationUserDAO.isPihUserDAO(AuthenticationUserDAO.java:24) at gov.hud.pih.eiv.web.authorization.AuthorizationProxy.isAuthorized(AuthorizationProxy.java:125) at gov.hud.pih.eiv.web.authorization.AuthorizationFilter.doFilter(AuthorizationFilter.java:224) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:246) at I am really stumped and can't figure out what could be causing this error. I am not able to reproduce the error on my machine but on production it is coming a lot of times. I am using iBatis in the whole application so there are no chances of my code not closing connections. We do have stored procedures that run for a long time before they return results (around 15 seconds). does anyone have any ideas on what could be causing this? I dont think raising the # of connections on the application server will fix this issue buecause if connections were running out then we'd see "Error on allocating connections"

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  • How do you match only valid roman numerals with a regular expression?

    - by Daniel Magliola
    Thinking about my other problem, i decided I can't even create a regular expression that will match roman numerals (let alone a context-free grammar that will generate them) The problem is matching only valid roman numerals. Eg, 990 is NOT "XM", it's "CMXC" My problem in making the regex for this is that in order to allow or not allow certain characters, I need to look back. Let's take thousands and hundreds, for example. I can allow M{0,2}C?M (to allow for 900, 1000, 1900, 2000, 2900 and 3000). However, If the match is on CM, I can't allow following characters to be C or D (because I'm already at 900). How can I express this in a regex? If it's simply not expressible in a regex, is it expressible in a context-free grammar? Thanks for any pointers!

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  • WPF: Is it possible to nest TreeView items with a binding expression?

    - by John Gietzen
    Lets say I have the following data: <XmlDataProvider x:Key="Values"> <x:XData> <folder name="C:"> <folder name="stuff" /> <folder name="things" /> <folder name="windows"> <folder name="system32" /> </folder> </folder> </x:XData> </XmlDataProvider> How can I get that into a treeview? I can't seem to grok hierarchical binding... I know that I can get it in there in C# code, but I wanted to do it with a binding expression.

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  • How do I get a value of a reference type in an Expression?

    - by Jon Kruger
    I have this method: public void DoSomething<T>(Expression<Func<T, object>> method) { } If this method is called like this: DoSomething(c => c.SomeMethod(new TestObject())); ... how do I get the value of the parameter that was passed into SomeMethod()? If the parameter is a value type, this works: var methodCall = (MethodCallExpression)method.Body; var parameterValue = ((ConstantExpression)methodCall.Arguments[0]).Value; However, when I pass in a reference type, methodCall.Arguments[0] is a MemberExpression, and I can't seem to figure out how to write code to get the value out of it.

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  • .Net Regular expression - how to do an exact match exclusion on a full string?

    - by Nathan Ridley
    I need a .Net regular expression that matches anything OTHER than the exact full string match specified. So basically: ^Index$ ... is the only exclusion I care about. Strings can start with, finish with or contain "Index", but not match exactly. My brain doesn't seem to be working today and I'm failing to work this one out. EDIT The answer MUST be via the pattern itself, as I am passing an argument to a third party library and do not have control over the process other than via the Regex pattern.

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