ReqLen constructor
Constrains the length (number of items).
len
the length or number of items; it must be >= 0.
blank
the error message in case of a null or empty input value.
diff
the error message if the length is different from len
.
Implementation
ReqLen(int len, {String? blank, String? diff})
: _reqLenVal = Pair(Req(blank: blank), Len(len, diff: diff));