On 06/03/2016 10:18 PM, Steven Schveighoffer wrote:
But you can get a standalone code unit that is part of a coded sequence
quite easily
foo(string s)
{
auto x = s[0];
dchar d = x;
}
I don' think we're disagreeing on anything.
I'm calling UTF-8 code units below 0x80 "standalone" code units. They're
never part of multibyte sequences. Your _dchar_convert returns them
unscathed.
Higher code units are always part of multibyte sequences (or invalid
already). Your function returns invalid code points for them.
_dchar_convert does exactly what I meant, except that I had in mind
returning the replacement character for non-standalone code units. But I
see that that may not be feasible, and it's probably not necessary.
[...]
So we need most efficient logic that does this:
if(c & 0x80)
return wchar(0xd800 + c);
Is this going to be faster than returning a constant invalid wchar?
else
return wchar(c);
More expensive, but more correct!
wchar to dchar conversion is pretty sound, as the surrogate pairs are
invalid code points for dchar.
-Steve
