isPositiveDecimalRate function

bool isPositiveDecimalRate(String rate)

Whether rate is a strictly-positive plain decimal string — the only kind of conversion rate that can be applied safely.

Returns false for a non-decimal, signed, empty, or whitespace string (anything foldEntryUsd would reject with a FormatException) and also for an exactly-zero rate ("0", "0.0", …): a zero rate converts every amount to zero, which would silently under-count rather than convert. Callers use this both to reject a bad rate at the boundary (before it is stored) and to fail closed at conversion time if an unvalidated rate is ever encountered.

Implementation

bool isPositiveDecimalRate(String rate) {
  final BigInt numerator;
  try {
    numerator = _parseDecimalRate(rate).num;
  } on FormatException {
    return false;
  }
  return numerator > BigInt.zero;
}