Int.pos constructor
Constrains data to positive integer numbers (zero included).
mal
"malformed", the error message for non-integer input values; the
default value is 'non-integer input value'.
neg
the error message if an input value is negative; the default value
is 'it cannot be negative'.
Implementation
Int.pos({String? mal, String? neg})
: this.min(0, mal: mal, small: neg ?? 'it cannot be negative');