What is a Portable Class Library?

Question

On MSDN I noticed a section about a Portable Class Library, under Version Information.

See System.Object for an example. http://msdn.microsoft.com/en-us/library/system.object.aspx

I did a brief Google search and couldn't find anything about the Portable Class Library. Does anyone here know what it is or where I could find more information about it?

Answer 1

UPDATE Oct 9 2017: Article comparing/constrasting .NET Core/Std/PCL UPDATE Nov 23 2016: Article by Rick Strahl

UPDATE Oct 29 2016: .NETStandard 1->2 FAQ UPDATE Oct 19 2016: This is the best interview/video I've seen to date covering .NET Standard 2.0

UPDATE Sep 27 2016: .NET Standard 2.0 announcement post has more good info

UPDATE Jun 6 2016: This article explains well how the .NETStandard library mechanism supersedes much of PCL

UPDATE Jul 10 2013: Excellent state of the PCL union summary blogpost from @shanselman with lots of concrete examples, screenshots and links. Puts any other answer here in the shade.

UPDATE May 20 2013:

• Very practical coverage of practical application and implications of this for cross-device stuff (think Xamarin Studio) in Tablet Show podcast with Atley Hunter. Key takeaway:- PCLs are a very useful constraint to impose on onself in cross-device scenarios.
• One of the libraries mentioned wrt that is the excellent MvvmCross which is discussed in a separate Tablet Show Episode 71 with it's author @Stuart Lodge. Only minor tweaking as described by Stuart here to environment setup is necessary to leverage PCLs for such purposes.

UPDATE Apr 19 2013: Excellent dense summary of how it all hangs together from Intellisense through to run time in a blog post by Simon Cooper

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Video: Channel 9 Visual Studio Toolbox show episode 14 June 2012

Video: Channel 9 Going Deep Show episode 27 Sep 2011

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UPDATE Sep 11 2012: Good high level blog post with pictures, diagrams and motivating examples showing how MVVM Light and RX use it

UPDATE Apr 11 2012: Very good end to end piece by Scott Hanselman that gets to the point in dev speak very quickly including screenshots here (also contains very insightful 'how to think of it' information and links to samples). Also includes a resources section at the end that pretty much duplicates this entire post :D

UPDATE Jul 9 2012: This blog series by Mircea Trofin of the dev team (one part so far) is the most complete coverage yet, including screenshots and detailed matrices showing available features across your selections if you're into that sort of thing.

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See Portable Library Tools anouncement blog post, which starts:-

The Portable Library Tools CTP adds a new "Portable Class Library" project template to Visual Studio that can be used to create class libraries in C# and VB that run on the various .NET platforms without recompiling.

It's used for creating a Class Library that targets multiple platforms (esp Silverlight variants such as WP7 and SL4, but including XNA on Xbox) at one time.

See also this InfoQ summary article

See also this release notice.

For down and dirty details, see Multi-Targeting Guidelines for Tools for Managed Code