The Base Class Library is the core of the CLR platform. It doesn’t matter if you are using .NET, Silverlight, or Mono, nor does it matter if you are a rich client or a web developer, if you are using the CLR then you are using the Base Class Library. So of course changes to the BCL are of particular importance to developers across the spectrum.
In order to be more transparent and to get feedback earlier in the development process, the Microsoft’s BCL team is previewing new classes on CodePlex. Here developers can try them out and, because it is open source, alter the classes for further experimentation.
The first class offered is BigRational. Based on a pair of BigIntegers, this allows you to store any rational number exactly. Because it stores the numerator and denominator separately, even fractions that cannot normally be stored exactly like 1/3 are supported.
Next up is LongPathDirectory and LongPathFile, which allows you to use up to 32,000 characters in the file path without the prefix “\\?\”. The inclusion of this is rather questionable for a number of reasons. First of all, it is a very Windows-specific feature in a time when the CLR is finding its way onto most platforms. Then there is the underlying question about compatibility. Most APIs and applications on the Windows platform are not long-path aware, making using long paths incredibly risky. You can learn more about some of the risks associated with Long Paths in .NET on the BCL blog. Finally, if Microsoft ever makes the necessary changes to the underlying Win32 API then these classes become unnecessary.
Finally, there is a library and matching command line application for working with Event Tracing for Windows. The library includes both low-level APIs for parsing raw event streams and a high-level object model for analysis.