Add RecipientAddress type.

src/zcash/Address.cpp

@@ -73,6 +73,25 @@ std::optional<SaplingPaymentAddress> UnifiedAddress::GetSaplingReceiver() const
     return std::nullopt;
 }
 
+std::optional<RecipientAddress> UnifiedAddress::GetPreferredRecipientAddress() const {
+    // Return the first receiver type we recognize; receivers are sorted in
+    // order from most-preferred to least.
+    std::optional<RecipientAddress> result;
+    for (const auto& receiver : *this) {
+        std::visit(match {
+            [&](const SaplingPaymentAddress& addr) { result = addr; },
+            [&](const CScriptID& addr) { result = addr; },
+            [&](const CKeyID& addr) { result = addr; },
+            [&](const UnknownReceiver& addr) { }
+        }, receiver);
+
+        if (result.has_value()) {
+            return result;
+        }
+    }
+    return std::nullopt;
+}
+
 bool HasKnownReceiverType(const Receiver& receiver) {
     return std::visit(match {
         [](const SaplingPaymentAddress& addr) { return true; },

src/zcash/Address.hpp

@@ -90,6 +90,12 @@ private:
     size_t cur;
 };
 
+/** A recipient address to which a unified address can be resolved */
+typedef std::variant<
+    CKeyID,
+    CScriptID,
+    libzcash::SaplingPaymentAddress> RecipientAddress;
+
 class UnifiedAddress {
     std::vector<Receiver> receivers;
 
@@ -148,6 +154,8 @@ public:
 
     std::optional<SaplingPaymentAddress> GetSaplingReceiver() const;
 
+    std::optional<RecipientAddress> GetPreferredRecipientAddress() const;
+
     friend inline bool operator==(const UnifiedAddress& a, const UnifiedAddress& b) {
         return a.receivers == b.receivers;
     }