The length operator
The length operator is denoted by the unary operator #. The length of a string is its number of bytes (that is, the usual meaning of string length when each character is one byte).
The length of a table t is defined to be any integer index n
such that t[n] is not null and t[n+1] is null;
moreover, if t[1] is null, n can be zero. For a regular
array, with non-null values from 1 to agiven n, its length is exactly that
n, the index of its last value. If the array has "holes" (that is, null
values between other non-null values), then #t can be any of the indices that
directly precedes a null value (that is, it may consider any such null value as the
end of the array).