What's New in the BCL in .NET 4.0 CTP [Justin Van Patten]

What's New in the BCL in .NET 4.0 CTP [Justin Van Patten]

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The Visual Studio 2010 and .NET Framework 4.0 CTP is available for download as of last week.  The CTP contains new functionality throughout the .NET Framework, including several new BCL features and improvements:

  • Code Contracts
    System.Diagnostics.Contracts provides a language-agnostic way to express coding assumptions in .NET programs.  The contracts take the form of pre-conditions, post-conditions, and object invariants.  Contracts act as checked documentation of your external and internal APIs.  The contracts are used to improve testing via runtime checking, enable static contract verification, and documentation generation.  We partnered with Microsoft Research to deliver this feature in .NET 4.0.  More information and tools are available on Microsoft Research’s code contracts website.  There’s also a highly-rated PDC session available online.

  • Parallel Extensions
    We worked with the Parallel Extensions team to add the Task Parallel Library (TPL), Coordination Data Structures, and Parallel LINQ (PLINQ) to the BCL in .NET 4.0.  This includes an improved ThreadPool scheduling algorithm for tasks, the static Parallel class, concurrent collections in System.Collections.Concurrent, and other coordination data structures such as LazyInit<T>, CountdownEvent, Barrier, SemaphoreSlim, SpinLock, SpinWait, and ManualResetEventSlim. More information is available over at the PFX team’s blog.  Also, check out Daniel Moth’s PDC session on Parallel Programming for Managed Developers with the Next Version of Microsoft Visual Studio.

  • BigInteger
    System.Numerics.BigInteger is an arbitrary-precision integer data type.  We worked with the Microsoft Solver Foundation team to deliver a highly performant big integer implementation.  BigInteger supports all the standard integer operations, including bit manipulation.  It can be used from any .NET language, and some of the new .NET languages—such as F# and IronPython—have support built-in to the language.

  • Memory Mapped Files
    System.IO.MemoryMappedFiles exposes the memory mapping functionality provided by Windows as first-class managed APIs.  Memory mapped files can be used to efficiently edit very large files and can also be used to create shared memory for inter-process communication.  Along with this feature, we’re also introducing System.IO.UnmanagedMemoryAccessor, a new class that enables random access to unmanaged memory similar to how UnmanagedMemoryStream enables sequential access to such memory.

  • ResourceManager Improvements
    The ResourceManager in System.Resources has been improved to respect the user’s preferred UI languages when looking for localized resources, instead of only using the CurrentUICulture’s parent chain.  This means if the user has specified that she prefers French and Spanish, the ResourceManager will look for French and Spanish resources before falling back to the neutral resources.  This change is present in Silverlight 2 as well as .NET 4.0.

  • Compression Improvements
    The compression algorithms in System.IO.Compression have been improved in .NET 4.0.  DeflateStream and GZipStream no longer inflate already compressed data.  This means that in most cases you’ll see much better compression ratios when using these streams on .NET 4.0.  We’ve also removed the 4 GB size limit, so you can now compress streams over 4 GB in size.

  • String Security Changes
    The default partial matching overloads on System.String (StartsWith, EndsWith, IndexOf, and LastIndexOf) have been changed to be culture-agnostic (ordinal) by default.  In addition, ToUpper and ToLower on System.String and System.Char have been changed to use the invariant culture instead of the current culture.  Although we have
    guidance and FxCop rules that recommend always using overloads that take a StringComparison parameter, unaware developers often just use the default overloads.  In previous versions of .NET, these default overloads do a culture-sensitive comparison using the current culture.  This can often lead to subtle bugs, most notably security vulnerabilities, when unaware developers use the default overloads to do security-sensitive string comparisons.  This change helps mitigate these vulnerabilities.  The change is present in both Silverlight 2 and .NET 4.0.  Even with these changes, our guidance still stands: whenever an overload exists that takes a StringComparison parameter, use it instead of an overload that does not take this parameter.  It makes your code clearer and easier to maintain.  This is especially important because the default overloads for String.Compare and String.CompareTo will remain culture-sensitive because these methods are most often used when sorting strings to be shown to the user.  We plan to add a compat switch in the beta that will allow an app to specify whether it wants the old behavior.

    UPDATE for .NET 4 Beta 1 In order to maintain high compatibility between .NET 4 and previous releases, we have decided to revert this change.  The behavior of String's default partial matching overloads and String and Char's ToUpper and ToLower methods now behave the same as they did in .NET 2.0/3.0/3.5.  The change back to the original behavior is present in .NET 4 Beta 1.  We apologize for any interim confusion this may cause.  We continue to recommend being explicit about the string comparison behavior you want, by always specifying a StringComparison value for the methods on String that accept it.

We’re also evaluating a number of potential new features and improvements for .NET 4.0 beta:

  • Variance annotations
    The next versions of C# and VB support safe co- and contra-variance for generic interface and delegate types.  Co-variance means that a generic of a type, e.g. an IEnumerable<String>, can be treated as a generic of any supertype, e.g. an IEnumerable<Object>.  Contra-variance means that a generic of a type, e.g. an Action<Object>, can be treated as a generic of a subtype, e.g. an Action<String>.  In C#, co-variance is annotated with the “out” keyword and contra-variance is annotated with the “in” keyword.  We are annotating several interfaces and delegates in the BCL for variance.  You can learn more about co- and contra-variance in Anders Hejlsberg’s PDC session on The Future of C#.

  • Tuples
    We are providing common tuple types in the BCL to facilitate language interoperability and to reduce duplication in the framework.  A tuple is a simple generic data structure that holds an ordered set of items of heterogeneous types.  Tuples are supported natively in languages such as F# and IronPython, but are also easy to use from any .NET language such as C# and VB.

  • SortedSet<T>
    We plan to add a SortedSet<T> collection along with an ISet<T> interface.  SortedSet<T> uses a self-balancing tree which maintains data in sorted order for performance guarantees with insertion, deletion, and searches.  Both the new SortedSet<T> and the existing HashSet<T> implement ISet<T>.

  • File System Enumeration Improvements
    We plan to add new file system enumeration APIs to System.IO.Directory and System.IO.DirectoryInfo that return IEnumerable<T>’s instead of arrays.  These new APIs are more efficient than the array-based APIs because they do not need to allocate a (potentially large) array and you can access the first results immediately instead of waiting for the entire enumeration to take place.  We’re also planning to add new convenience APIs for efficiently reading, writing, and appending lines from/to a text file using IEnumerable<String>.  These new APIs are useful in LINQ scenarios where you may want to quickly and efficiently query the contents of a text file and write out the results to a log file without allocating any arrays.

There are also a bunch of improvements to the CLR in .NET 4.0.  Here’s a high-level summary:

You can learn more about the next version of the CLR in Joshua Goodman’s PDC session on Microsoft .NET Framework: CLR Futures.

Over the next couple of weeks we’ll be posting more about the new functionality that’s available in the CTP.  Do note that we’re working on many other improvements for 4.0 that we’re not quite ready to announce just yet.

As always, we’d love to hear what you think of the CTP and announcements so far.

  • Hi Andrew,

    >>>>> So why is it that String.Replace(String,String) still doesn't take a StringComparison arg?  The String.Contains method is another oversight.

    This indeed has been a longstanding oversight that we’ve been meaning to address for quite some time.  Unfortunately the nature of our 3.0 and 3.5 releases (layer cake model) means we haven’t been able to address some of these oversights since we released 2.0.  The good news is that we’re planning to finally address this in 4.0 :-)

    >>>>> However, I think we all know the dangers of people recompiling their .NET 1/2/3 code against .NET 4.0 and suddenly getting the different behaviour.  Much migration guidance needs to be given.

    We are very mindful of this.  In addition to guidance, we’ll also provide an app compat switch that will allow older apps to specify that they want the old behavior.



  • Hi Stu,

    >>>>> I've been reading with interest about the SSE support in Mono... any chance similar changes could appear in MS's CLR?

    Unfortunately not for 4.0.  But this is something we’ll be evaluating for future releases.



  • Hi Anders,

    >>>>> Regarding the string class, I'd like to request that string.Contains is overloaded to take params (i.e. "contains all these strings" instead of just one operator). Also string.ContainsAny with params would be nice as it's a very common pattern among developers to check a string for either N or any inclusive instances of other strings.

    Thanks for the suggestions.  We’ll see if we can fit some of these in for 4.0.



  • Hi Steven,

    It's a CLI limitation that co/contravariance is supported only on interfaces and delegates. This form of variance is already supported in the CLR and can be used in IL with the +/- notation.

    Regarding the C# change -- they've added keywords to allow use of variance, but C# (and any .NET language) is limited by the CLI/CLR support. That is, unless they want to add extra support on top, which I understand Eiffel .NET does.

    At the moment, there are no plans for broader variance support, but if you haven't already, you may want to check out Eric Lippert's blog series on co/contravariance. In the comments sections, you'll see a lot of requests and discussion around broader variance support...and an extended discussion of the issues involved.



  • > Regarding the string class, I'd like to request that string.Contains is overloaded to take params (i.e. "contains all these strings" instead of just one operator).

    string s;


    new[] { "foo", "bar", "baz" }.All(sub => s.Contains(sub))

    > Also string.ContainsAny with params would be nice as it's a very common pattern among developers to check a string for either N or any inclusive instances of other strings.

    new[] { "foo", "bar", "baz" }.Any(sub => s.Contains(sub))

  • Obviously I&#39;ve been looking at the proposed C# 4.0 features pretty carefully, and I promise I&#39;ll

  • Great news about the tuples. I'm looking forward towards quite a lot of F#/C# mixed code now :)

    Regarding contracts: are you going to use them throughout the BCL itself (and other parts of the FCL) as well? I recall seeing some seemingly contract-related attributes on the (internal) BigInteger class in 3.5 - more to come? Obviously, contracts, and particularly the static type checking feature - are only truly useful when they are used from top to bottom.

    Also, since people above remind of some common refactoring requests, let me add one as well: generify more BCL classes! I mean stuff like WeakReference<T>, Type<T>, and so on.

  • int19h,

    We will be adding contracts throughout as much of the BCL as we can in .NET 4.0, but we won't have 100% coverage.  We're also getting the rest of the FCL on board.  This will be a phased approach over the next couple of releases, where each release will have better coverage throughout .NET and more streamlined tools.

    We don't have plans to add  WeakReference<T> or Type<T> in 4.0, but these (and some other generic types) are things we are considering for the future.  Thanks for the suggestions.



  • Justin,

    Great feedback and great news.



  • Design by Contract with .NET 4.0

  • Hi, this sounds all very exciting!

    > In Process Side-by-Side: support for multiple CLR versions running in the same process.

    Does this mean that it may be possible to (safely) write shell extensions in .NET starting with 4.0?

  • I’ve just found an interesting post with some of the new stuff we’ll have on the next version of the

  • I’ve just found an interesting post with some of the new stuff we’ll have on the next version of the

  • .NET What's New in the BCL in .NET 4.0 NetMon API &#8211; Capture, Parse and and Capture File Access

  • .NETWhat'sNewintheBCLin.NET4.0NetMonAPI–Capture,ParseandandCaptureFileAccess(wi...

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