Windows Application Data Directory

The way the do this on Windows is to use the ApplicationData environment variable. If you were using C# you can get the folder it maps to using System.Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), googling for the Ruby equivalent it's ENV['APPDATA']. In English-language Windows it maps to:

C:\Users\%username%\AppData\Roaming\ (on Vista and Windows 7)

C:\Documents and Settings\%username%\Application Data\ (On XP)

It may map to a different folder in other languages, but as long as you get the directory from the environment variable and not hard-code it then it doesn't really make a difference. If you create a folder in there for your app and store the data there, Vista and 7 will allow read and write access to it without giving UAC prompts.

Offhand, I'm not sure how Ruby handles expand_path on ~ for Windows. Windows has functions like SHGetSpecialFolderPath, and SHGetSpecialFolderLocation for this kind of thing. It would seem like an obvious thing for expand_path to use one of those, but I don't know whether it does for sure.

For Vista and Windows 7 and Windows XP,

    char appdir[MAX_PATH];          size_t requiredSize;    errno_t err= getenv_s( &requiredSize, appdir, MAX_PATH, "appdata" );

seems simpler than using deprecated APIs or ones that don't work on Windows XP.