I hadn't realised that WordPress had added a native function for it to the Codex, but for some odd reason the page is blank. Does that mean the functionality is still coming or the page was added by mistake?
http://codex.wordpress.org/Function_Reference/get_permalink_by_slug
It's blank because it doesn't exist. If you change that function name to any random name you like you'll still see a blank page (unless of course the name you change it to is a real function).