My investigations regarding archiving on OS X:
1. NSArchiver stores all strings in Utf-8.
This is inefficient for strings which contain mainly non-european
characters (e.g. Chinese or Thai) as one character will use 3 bytes (Utf-16
would use only 2).
Corollary: It cannot store strings which contain illegal Unicode chars.
2. NSKeyedArchiver seems to be ok.
But it does create unnecessary data. E.g. in the case of an array
containing identical objects, like:
NSArray *a = @[ @"a", @"a", ...., @"a"];
With 1 000 000 items it creates 10,000,395 bytes - my version creates
only 1 000 332 bytes
and the output is still readable by NSKeyedUnarchiver.
3, NSKeyedUnarchiver has several bugs.
The string $null is converted to nil.
Very harmful if this string is part of a collection (like array, set or
dictionary).
If the key in: encodeXXX:forKey: starts with an "$" NSKeyedArchiver
correctly mangles this by prefixing
another "$". But NSKeyedUnarchiver does not find these mangled keys and
returns nil or 0.
I have not reported these bugs, as I am convinced that Apple has no interest in
fixing these problems.
Gerriet.
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