On success, the function returns the number of variables filled. This count can match the expected number of readings or fewer, even zero, if a matching failure happens.
A FormatException if S.length == 0 and fmt has format specifiers.
The format string can be checked at compile-time (see format for details):
string s = "hello!124:34.5"; string a; int b; double c; s.formattedRead!"%s!%s:%s"(a, b, c); assert(a == "hello" && b == 124 && c == 34.5);
Reads characters from input range r, converts them according to fmt, and writes them to args.