From 880f9adcd38805e5d1a9fd26dddc2c074bf12904 Mon Sep 17 00:00:00 2001
From: Antioch Peverell <apeverell@protonmail.com>
Date: Sat, 1 Aug 2020 15:19:17 +0100
Subject: [PATCH] use AsRef in cut_through for flexibility (#3411)

and use fold() to get len of inputs, outputs, kernels
---
 core/src/core/transaction.rs | 62 ++++++++++++++++++++----------------
 1 file changed, 34 insertions(+), 28 deletions(-)

diff --git a/core/src/core/transaction.rs b/core/src/core/transaction.rs
index 0e51da452d..38f198f544 100644
--- a/core/src/core/transaction.rs
+++ b/core/src/core/transaction.rs
@@ -1290,26 +1290,33 @@ impl Transaction {
 /// eliminating any input/output pairs with input spending output.
 /// Returns new slices with cut-through elements removed.
 /// Also returns slices of the cut-through elements themselves.
+/// Note: Takes slices of _anything_ that is AsRef<Commitment> for greater flexibility.
+/// So we can cut_through inputs and outputs but we can also cut_through inputs and output identifiers.
+/// Or we can get crazy and cut_through inputs with other inputs to identify intersection and difference etc.
 ///
 /// Example:
 /// Inputs: [A, B, C]
 /// Outputs: [C, D, E]
 /// Returns: ([A, B], [D, E], [C], [C]) # element C is cut-through
-pub fn cut_through<'a>(
-	inputs: &'a mut [Input],
-	outputs: &'a mut [Output],
-) -> Result<(&'a [Input], &'a [Output], &'a [Input], &'a [Output]), Error> {
-	// Make sure inputs and outputs are sorted consistently by commitment.
-	inputs.sort_unstable_by_key(|x| x.commitment());
-	outputs.sort_unstable_by_key(|x| x.commitment());
+pub fn cut_through<'a, 'b, T, U>(
+	inputs: &'a mut [T],
+	outputs: &'b mut [U],
+) -> Result<(&'a [T], &'b [U], &'a [T], &'b [U]), Error>
+where
+	T: AsRef<Commitment> + Ord,
+	U: AsRef<Commitment> + Ord,
+{
+	// Make sure inputs and outputs are sorted consistently as we will iterate over both.
+	inputs.sort_unstable_by_key(|x| *x.as_ref());
+	outputs.sort_unstable_by_key(|x| *x.as_ref());
 
 	let mut inputs_idx = 0;
 	let mut outputs_idx = 0;
 	let mut ncut = 0;
 	while inputs_idx < inputs.len() && outputs_idx < outputs.len() {
 		match inputs[inputs_idx]
-			.partial_cmp(&outputs[outputs_idx])
-			.expect("compare input to output")
+			.as_ref()
+			.cmp(&outputs[outputs_idx].as_ref())
 		{
 			Ordering::Less => {
 				inputs.swap(inputs_idx - ncut, inputs_idx);
@@ -1370,15 +1377,16 @@ pub fn aggregate(txs: &[Transaction]) -> Result<Transaction, Error> {
 	} else if txs.len() == 1 {
 		return Ok(txs[0].clone());
 	}
-	let mut n_inputs = 0;
-	let mut n_outputs = 0;
-	let mut n_kernels = 0;
-	for tx in txs.iter() {
-		n_inputs += tx.inputs().len();
-		n_outputs += tx.outputs().len();
-		n_kernels += tx.kernels().len();
-	}
 
+	let (n_inputs, n_outputs, n_kernels) =
+		txs.iter()
+			.fold((0, 0, 0), |(inputs, outputs, kernels), tx| {
+				(
+					inputs + tx.inputs().len(),
+					outputs + tx.outputs().len(),
+					kernels + tx.kernels().len(),
+				)
+			});
 	let mut inputs: Vec<Input> = Vec::with_capacity(n_inputs);
 	let mut outputs: Vec<Output> = Vec::with_capacity(n_outputs);
 	let mut kernels: Vec<TxKernel> = Vec::with_capacity(n_kernels);
@@ -1498,17 +1506,9 @@ pub struct Input {
 impl DefaultHashable for Input {}
 hashable_ord!(Input);
 
-// Inputs can be compared to outputs.
-impl PartialEq<Output> for Input {
-	fn eq(&self, other: &Output) -> bool {
-		self.commitment() == other.commitment()
-	}
-}
-
-// Inputs can be compared to outputs.
-impl PartialOrd<Output> for Input {
-	fn partial_cmp(&self, other: &Output) -> Option<Ordering> {
-		Some(self.commitment().cmp(&other.commitment()))
+impl AsRef<Commitment> for Input {
+	fn as_ref(&self) -> &Commitment {
+		&self.commit
 	}
 }
 
@@ -1714,6 +1714,12 @@ pub struct Output {
 impl DefaultHashable for Output {}
 hashable_ord!(Output);
 
+impl AsRef<Commitment> for Output {
+	fn as_ref(&self) -> &Commitment {
+		&self.commit
+	}
+}
+
 impl ::std::hash::Hash for Output {
 	fn hash<H: ::std::hash::Hasher>(&self, state: &mut H) {
 		let mut vec = Vec::new();