Am 31.08.2011, 08:12 Uhr, schrieb Don <nos...@nospam.com>:
I didn't understand this line of the paper. Although what they propose clearly works for caching, I don't see how it can possibly apply to the log file example.
A log file is appended to and never read from. It is not part of the program state, like a temporary or cache file would be. Writing the log does not change an observable state in the program. Compare the file to a memory location in your program. Usually you don't access arbitrary raw memory addresses like that private member of an object that caches a value, but you could. Observational purity only works because we restrict ourselves to operations that are in the spirit of things like 'private members' or 'log files'. Admittedly it is possible for a language/compiler to disallow unsafe pointer operations, but not keep you from reading your log files back in.
