Amount::{zero, is_positive, is_negative}

zcash_primitives/src/transaction/builder.rs

@@ -79,7 +79,7 @@ impl SaplingOutput {
             Some(g_d) => g_d,
             None => return Err(Error(ErrorKind::InvalidAddress)),
         };
-        if value.0 < 0 {
+        if value.is_negative() {
             return Err(Error(ErrorKind::InvalidAmount));
         }
 
@@ -288,7 +288,7 @@ impl<R: RngCore + CryptoRng> Builder<R> {
         to: &TransparentAddress,
         value: Amount,
     ) -> Result<(), Error> {
-        if value.0 < 0 {
+        if value.is_negative() {
             return Err(Error(ErrorKind::InvalidAmount));
         }
 

zcash_primitives/src/transaction/components/amount.rs

@@ -8,6 +8,11 @@ const MAX_MONEY: i64 = 21_000_000 * COIN;
 pub struct Amount(pub i64);
 
 impl Amount {
+    /// Returns a zero-valued Amount.
+    pub const fn zero() -> Self {
+        Amount(0)
+    }
+
     // Read an Amount from a signed 64-bit little-endian integer.
     pub fn read_i64<R: Read>(mut reader: R, allow_negative: bool) -> io::Result<Self> {
         let amount = reader.read_i64::<LittleEndian>()?;
@@ -39,6 +44,18 @@ impl Amount {
             ))
         }
     }
+
+    /// Returns `true` if `self` is positive and `false` if the number is zero or
+    /// negative.
+    pub const fn is_positive(self) -> bool {
+        self.0.is_positive()
+    }
+
+    /// Returns `true` if `self` is negative and `false` if the number is zero or
+    /// positive.
+    pub const fn is_negative(self) -> bool {
+        self.0.is_negative()
+    }
 }
 
 #[cfg(test)]

zcash_primitives/src/transaction/mod.rs

@@ -112,7 +112,7 @@ impl TransactionData {
             vout: vec![],
             lock_time: 0,
             expiry_height: 0,
-            value_balance: Amount(0),
+            value_balance: Amount::zero(),
             shielded_spends: vec![],
             shielded_outputs: vec![],
             joinsplits: vec![],
@@ -190,7 +190,7 @@ impl Transaction {
             let so = Vector::read(&mut reader, OutputDescription::read)?;
             (vb, ss, so)
         } else {
-            (Amount(0), vec![], vec![])
+            (Amount::zero(), vec![], vec![])
         };
 
         let (joinsplits, joinsplit_pubkey, joinsplit_sig) = if version >= 2 {