What is the meaning of returning value in failed blackjack algorithm? about coinselect HOT 3 CLOSED

@Runn1ng when possible, a fee is returned to indicate to a higher-level UI or algorithm what the prospective fees would at least be given the current set of inputs and outputs.

This can provide support for users to iteratively build transactions, seeing what the fees might be, even if a valid, balanced transaction doesn't exist [yet].

In the blackjack algorithm, it is less useful, but it was an interface I maintained.

If no fee is returned, it likely means that the inputs given are entirely invalid, not just that there doesn't exist a valid subset.

from coinselect.

For example, I want to send a transaction with 200 satoshi/byte fee, but I can't afford it.
Without fee being returned, I wouldn't be able to inform the user "transaction fee would be X, you only have Y", I could only say "not enough funds".
It isn't 100% representative of what the fee "would have" been, but, it is informative.

from coinselect.

OK, that makes some sense, altough I am still not sure if it doesn't end up more confusing than informative.

from coinselect.