.NET BCL source code

Source code for .NET Base Class Library has been made available for debugging sessions in VS2008. It would download one file at a time as they are needed. Since then John Robbins and Karem Kusmezer have create a tool to download all the source files without hassle, great work! The tool is NetMassDownloader.

Use it whilst it is still working :). Download, unpack, and run:

NetMassDownloader.exe -output bcl
    -d C:\Windows\Microsoft.NET\Framework\v2.0.50727

I executed in in Windows XP as a limited user and have seen numerous failure messages printed out. Nevertheless, 120MB of data was downloaded and I had all the files I wanted. The authors advise though to run it as a privileged process (at least on Vista).

The most interesting parts are bcl/redbits/ndp/clr/src/BCL/System and bcl/redbits/ndp/fx/src where bcl is the name of the directory you provided after -output switch. Together they are about 75MB.

It was pretty interesting to read the implementation of the classes I had been using for so long: String, Hashtable, Arraylist. They are easy to understand, with lots of comments, and of course in C#.

The classes I have read are all pretty basic and no wonder there are lots of pointers and calls into unmanaged code, but it is still readable.

One surprising thing, but obvious after knowing it, is that " s ".Trim() will not create a new string "s", but return a slice, an object that holds a reference to the original string and knows where are the beginning and the end. This is possible thanks to the immutability of strings. I bet the substring method is implemented like this too.

There are also some monster methods to be seen. One example is internal HttpListener.HandleAuthenticate spanning more than half a thousand lines.

BTW source code for mono is available at mono-project.com/AnonSVN. Source for mono's BCL is under mcs/class/corlib. It might be interesting to compare the two.