How is this possible not to include stdlib (mscorlib.dll) to my C# application when compiling it? As far as I know, all classes inherit System.Object class, which is defined in mscorlib.dll. What is more - types such as int are just aliases e.g. for System.Int32, which are also defined in mscorlib. Is this option ever used?
Yes, it is used by anybody that compiles a program that doesn't run with the desktop version of the CLR. Like Silverlight, it targets .NETCore, or the Micro Framework. They have their own mscorlib.dll, of course with System.Object defined.
Here's the compiler command line of a sample Silverlight project:
C:\Windows\Microsoft.NET\Framework\v4.0.30319\Csc.exe /noconfig /nowarn:1701,1702
/nostdlib+ /errorreport:prompt /warn:4 /define:DEBUG;TRACE;SILVERLIGHT
/reference:"c:\Program Files\Reference Assemblies\Microsoft\Framework\Silverlight\v4.0\mscorlib.dll"
etc...
According to the docs
http://msdn.microsoft.com/en-us/library/fa13yay7(VS.80).aspx
You use it if you are trying to replace the System classes.
You may also want to use it if you want to build to deploy against an older framework version. Visual Studio (15, anyway) uses this option when building a project that you configured to target an older framework version. Instead of using the standard mscore, it uses one from Reference Assemblies/Microsoft/Framework/vx.y
From MSDN - "Use this option if you want to define or create your own System namespace and objects.". Fair enough - I won't be doing that any time soon, tho'. :)
来源：https://stackoverflow.com/questions/3383130/c-sharp-compiler-nostdlib-option