What happens to C# 4 optional parameters when compiling against 3.5?

Here’s a method declaration that uses optional parameters: public Path Copy( Path destination, bool overwrite = false , bool recursive = false ) Something you may not know is that Visual Studio 2010 will let you compile this against .NET 3.5, with no error or warning. You may be wondering (as I was) how it does that. Well, it takes the easy and rather obvious way of not trying to be too smart and just ignores the optional parameters. So if you’re compiling against 3.5 from Visual Studio 2010, the above code is equivalent to: public Path Copy( Path destination, bool overwrite, bool recursive) The parameters are not optional (no such thing in C# 3), and no overload gets magically created for you. If you’re building a library that is going to have…(read more)