Merge bitcoin-core#711: refactor: Disable unused special members functions in UnlockContext

9fa43b5 refactor: Disable unused special members functions in `UnlockContext` (Hennadii Stepanov)

Pull request description:

  Also `UnlockContext::valid` and `UnlockContext::relock` are `const` now.

ACKs for top commit:
  achow101:
    ACK 9fa43b5
  john-moffett:
    ACK 9fa43b5
  furszy:
    ACK 9fa43b5

Tree-SHA512: 6d9fa8208676b9bd5d85b73cb2d3136e7f28ef59e68ee34915ec598458868e302a80b9ef1384c0bf7a4c42f936830c3add9662ca0bae73860a55a25cc374b699

Author: achow101

src/qt/walletmodel.cpp

@@ -477,13 +477,6 @@ WalletModel::UnlockContext::~UnlockContext()
     }
 }
 
-void WalletModel::UnlockContext::CopyFrom(UnlockContext&& rhs)
-{
-    // Transfer context; old object no longer relocks wallet
-    *this = rhs;
-    rhs.relock = false;
-}
-
 bool WalletModel::bumpFee(uint256 hash, uint256& new_hash)
 {
     CCoinControl coin_control;

src/qt/walletmodel.h

@@ -111,7 +111,7 @@ class WalletModel : public QObject
     bool setWalletLocked(bool locked, const SecureString &passPhrase=SecureString());
     bool changePassphrase(const SecureString &oldPass, const SecureString &newPass);
 
-    // RAI object for unlocking wallet, returned by requestUnlock()
+    // RAII object for unlocking wallet, returned by requestUnlock()
     class UnlockContext
     {
     public:
@@ -120,18 +120,16 @@ class WalletModel : public QObject
 
         bool isValid() const { return valid; }
 
-        // Copy constructor is disabled.
+        // Disable unused copy/move constructors/assignments explicitly.
         UnlockContext(const UnlockContext&) = delete;
-        // Move operator and constructor transfer the context
-        UnlockContext(UnlockContext&& obj) { CopyFrom(std::move(obj)); }
-        UnlockContext& operator=(UnlockContext&& rhs) { CopyFrom(std::move(rhs)); return *this; }
+        UnlockContext(UnlockContext&&) = delete;
+        UnlockContext& operator=(const UnlockContext&) = delete;
+        UnlockContext& operator=(UnlockContext&&) = delete;
+
     private:
         WalletModel *wallet;
-        bool valid;
-        mutable bool relock; // mutable, as it can be set to false by copying
-
-        UnlockContext& operator=(const UnlockContext&) = default;
-        void CopyFrom(UnlockContext&& rhs);
+        const bool valid;
+        const bool relock;
     };
 
     UnlockContext requestUnlock();