parse int error

[Peter Eisenhower]

I am confused as to why I cannot pass the return of the tag 
attribute directly into the parse int.

// This works
 string s = xml.tag.attr["key"];
 int key = parse!int(s);
// Compile error on these
int key = parse!int(xml.tag.attr["key"]);
int key = parse!int(cast(string) cml.tag.attr["key"]);