Fun with IDisposable

Written and © by P. Most (11.01.2021, 16:32:21)

Problem

When I had a couple of times to programmatically change the current directory and then restore it to it's original value I dutifully wrote:


void ChangeCurrentDirectory( string newDirectory ) {
	var oldDirectory = Directory.GetCurrentDirectory();
	Directory.SetCurrentDirectory( newDirectory );
	
	// Do something now which relies on the current directory pointing to a specific directory...
	
	Directory.SetCurrentDirectory( oldDirectory );
}

Of course this isn't exception safe and quite annoying if you have to write it a couple of times. So I thought: "How would I solve this in C++ with RAII?" This is actually quite easy of course. You save the current directory in the constructor and restore it in the destructor. So the next question was: "What does C# have which comes close to that?" The answer is IDisposable. So I wrote this little class:

Solution


public class CurrentDirectoryChanger : IDisposable {
	private string _oldCurrentDirectory;

	public CurrentDirectoryChanger( string newCurrentDirectory ) {
		_oldCurrentDirectory = Directory.GetCurrentDirectory();
		Directory.SetCurrentDirectory( newCurrentDirectory );
	}

	public void Dispose() {
		Directory.SetCurrentDirectory( _oldCurrentDirectory );
	}
}

which allows me to use it like this:


using ( new CurrentDirectoryChanger( newCurrentDirectory )) {

	// Do something now which relies on the current directory pointing to a specific directory...

}

Even though this might not be in the spirit of the using statement, because according to "The C# Programming Language, 8.13 The using Statement":

"The using statement obtains one or more resources, executes a statement, and the disposes of the resource"

I still like it and sometimes you have to think out of the box to make your life easier.