add OutcomeIndex alias for outcome indexes

src/contract/mod.rs

@@ -19,6 +19,10 @@ use std::collections::{BTreeMap, BTreeSet};
 /// index in the sorted set of players.
 pub type PlayerIndex = usize;
 
+/// A type alias for clarity. Players in the DLC are often referred to by their
+/// index in the sorted set of players.
+pub type OutcomeIndex = usize;
+
 /// Represents a mapping of player to payout weight for a given outcome.
 ///
 /// A player's payout under an outcome is proportional to the size of their payout weight
@@ -82,7 +86,7 @@ pub struct ContractParameters {
 #[derive(Clone, Copy, Debug, Ord, PartialOrd, Eq, PartialEq, Hash)]
 pub enum Outcome {
     /// Indicates the oracle attested to a particular outcome of the given index.
-    Attestation(usize),
+    Attestation(OutcomeIndex),
 
     /// Indicates the oracle failed to attest to any outcome, and the event expiry
     /// timelock was reached.

src/contract/outcome.rs

@@ -8,7 +8,7 @@ use secp::{Point, Scalar};
 use std::collections::{BTreeMap, BTreeSet};
 
 use crate::{
-    contract::{ContractParameters, Outcome},
+    contract::{ContractParameters, Outcome, OutcomeIndex},
     errors::Error,
     spend_info::{FundingSpendInfo, OutcomeSpendInfo},
 };
@@ -226,7 +226,7 @@ pub(crate) fn verify_outcome_tx_partial_signatures(
 pub(crate) struct OutcomeSignatures {
     /// A set of adaptor signatures which can be unlocked by the oracle's attestation
     /// for each outcome.
-    pub(crate) outcome_tx_signatures: BTreeMap<usize, AdaptorSignature>,
+    pub(crate) outcome_tx_signatures: BTreeMap<OutcomeIndex, AdaptorSignature>,
 
     /// The complete signature on the expiry transaction. This is `None` if the
     /// [`ContractParameters::outcome_payouts`] field does not contain an
@@ -312,7 +312,7 @@ pub(crate) fn verify_outcome_tx_aggregated_signatures(
     params: &ContractParameters,
     our_pubkey: Point,
     outcome_build_out: &OutcomeTransactionBuildOutput,
-    outcome_tx_signatures: &BTreeMap<usize, AdaptorSignature>,
+    outcome_tx_signatures: &BTreeMap<OutcomeIndex, AdaptorSignature>,
     expiry_tx_signature: Option<CompactSignature>,
 ) -> Result<(), Error> {
     let funding_spend_info = &outcome_build_out.funding_spend_info;

src/lib.rs

@@ -27,7 +27,7 @@ use std::{
     collections::{BTreeMap, BTreeSet},
 };
 
-pub use contract::{ContractParameters, Outcome, PlayerIndex, SigMap, WinCondition};
+pub use contract::{ContractParameters, Outcome, OutcomeIndex, PlayerIndex, SigMap, WinCondition};
 pub use oracles::EventAnnouncement;
 pub use parties::{MarketMaker, Player};
 
@@ -420,7 +420,7 @@ pub struct ContractSignatures {
     /// [`EventAnnouncement::outcome_messages`]. Each adaptor signature can be decrypted
     /// by the [`EventAnnouncement`]'s oracle producing an attestation signature using
     /// [`EventAnnouncement::attestation_secret`].
-    pub outcome_tx_signatures: BTreeMap<usize, AdaptorSignature>,
+    pub outcome_tx_signatures: BTreeMap<OutcomeIndex, AdaptorSignature>,
     /// A set of signatures needed for broadcasting split transactions. Each signature
     /// is specific to a certain combination of player and outcome.
     pub split_tx_signatures: BTreeMap<WinCondition, CompactSignature>,
@@ -492,7 +492,10 @@ impl SignedContract {
     }
 
     /// Return an unsigned outcome transaction.
-    pub fn unsigned_outcome_tx<'a>(&'a self, outcome_index: usize) -> Option<&'a Transaction> {
+    pub fn unsigned_outcome_tx<'a>(
+        &'a self,
+        outcome_index: OutcomeIndex,
+    ) -> Option<&'a Transaction> {
         self.dlc
             .outcome_tx_build
             .outcome_txs()
@@ -503,7 +506,7 @@ impl SignedContract {
     /// to a specific outcome.
     pub fn signed_outcome_tx(
         &self,
-        outcome_index: usize,
+        outcome_index: OutcomeIndex,
         attestation: impl Into<MaybeScalar>,
     ) -> Result<Transaction, Error> {
         let attestation = attestation.into();

src/oracles.rs

@@ -1,5 +1,7 @@
 use secp::{MaybePoint, MaybeScalar, Point, Scalar};
 
+use crate::OutcomeIndex;
+
 /// An oracle's announcement of a future event.
 #[derive(Debug, Clone)]
 pub struct EventAnnouncement {
@@ -18,7 +20,7 @@ pub struct EventAnnouncement {
 
 impl EventAnnouncement {
     /// Computes the oracle's locking point for the given outcome index.
-    pub fn attestation_lock_point(&self, index: usize) -> Option<MaybePoint> {
+    pub fn attestation_lock_point(&self, index: OutcomeIndex) -> Option<MaybePoint> {
         let msg = &self.outcome_messages.get(index)?;
 
         let e: MaybeScalar = musig2::compute_challenge_hash_tweak(