isPositive method

FieldValidator<T, num> isPositive([
  1. MessageCallBack<num>? message
])

check if the value is positive

Implementation

FieldValidator<T, num> isPositive([MessageCallBack<num>? message]) {
  return next((messages, value) {
    if (value.isNegative) {
      return message?.call(messages, value) ?? messages.isPositive;
    }
    return null;
  });
}