Style cleanup.

1) Convert iterator-based for loops to C++11 foreach loops.
2) Convert "void operator=" to "T& operator=".
3) Switch from copy operators from private to public deleted.
4) Switch from empty ctors / dtors to "= default" where appropriate.

PiperOrigin-RevId: 246679195

18 files changed, 164 insertions, 163 deletions

diff --git a/db/db_impl.cc b/db/db_impl.cc
index 761ebf6..82be594 100644
--- a/db/db_impl.cc
+++ b/db/db_impl.cc
@@ -1469,7 +1469,7 @@ Status DB::Delete(const WriteOptions& opt, const Slice& key) {
   return Write(opt, &batch);
 }
 
-DB::~DB() {}
+DB::~DB() = default;
 
 Status DB::Open(const Options& options, const std::string& dbname, DB** dbptr) {
   *dbptr = nullptr;
@@ -1514,7 +1514,7 @@ Status DB::Open(const Options& options, const std::string& dbname, DB** dbptr) {
   return s;
 }
 
-Snapshot::~Snapshot() {}
+Snapshot::~Snapshot() = default;
 
 Status DestroyDB(const std::string& dbname, const Options& options) {
   Env* env = options.env;
diff --git a/db/db_test.cc b/db/db_test.cc
index 78296d5..e7386f7 100644
--- a/db/db_test.cc
+++ b/db/db_test.cc
@@ -2024,19 +2024,19 @@ class ModelDB : public DB {
   };
 
   explicit ModelDB(const Options& options) : options_(options) {}
-  ~ModelDB() {}
+  ~ModelDB() override = default;
   virtual Status Put(const WriteOptions& o, const Slice& k, const Slice& v) {
     return DB::Put(o, k, v);
   }
-  virtual Status Delete(const WriteOptions& o, const Slice& key) {
+  Status Delete(const WriteOptions& o, const Slice& key) override {
     return DB::Delete(o, key);
   }
-  virtual Status Get(const ReadOptions& options, const Slice& key,
-                     std::string* value) {
+  Status Get(const ReadOptions& options, const Slice& key,
+             std::string* value) override {
     assert(false);  // Not implemented
     return Status::NotFound(key);
   }
-  virtual Iterator* NewIterator(const ReadOptions& options) {
+  Iterator* NewIterator(const ReadOptions& options) override {
     if (options.snapshot == nullptr) {
       KVMap* saved = new KVMap;
       *saved = map_;
@@ -2047,16 +2047,16 @@ class ModelDB : public DB {
       return new ModelIter(snapshot_state, false);
     }
   }
-  virtual const Snapshot* GetSnapshot() {
+  const Snapshot* GetSnapshot() override {
     ModelSnapshot* snapshot = new ModelSnapshot;
     snapshot->map_ = map_;
     return snapshot;
   }
 
-  virtual void ReleaseSnapshot(const Snapshot* snapshot) {
+  void ReleaseSnapshot(const Snapshot* snapshot) override {
     delete reinterpret_cast<const ModelSnapshot*>(snapshot);
   }
-  virtual Status Write(const WriteOptions& options, WriteBatch* batch) {
+  Status Write(const WriteOptions& options, WriteBatch* batch) override {
     class Handler : public WriteBatch::Handler {
      public:
       KVMap* map_;
@@ -2070,15 +2070,15 @@ class ModelDB : public DB {
     return batch->Iterate(&handler);
   }
 
-  virtual bool GetProperty(const Slice& property, std::string* value) {
+  bool GetProperty(const Slice& property, std::string* value) override {
     return false;
   }
-  virtual void GetApproximateSizes(const Range* r, int n, uint64_t* sizes) {
+  void GetApproximateSizes(const Range* r, int n, uint64_t* sizes) override {
     for (int i = 0; i < n; i++) {
       sizes[i] = 0;
     }
   }
-  virtual void CompactRange(const Slice* start, const Slice* end) {}
+  void CompactRange(const Slice* start, const Slice* end) override {}
 
  private:
   class ModelIter : public Iterator {
diff --git a/db/fault_injection_test.cc b/db/fault_injection_test.cc
index 7088ea7..5b31bb8 100644
--- a/db/fault_injection_test.cc
+++ b/db/fault_injection_test.cc
@@ -109,11 +109,11 @@ class TestWritableFile : public WritableFile {
  public:
   TestWritableFile(const FileState& state, WritableFile* f,
                    FaultInjectionTestEnv* env);
-  virtual ~TestWritableFile();
-  virtual Status Append(const Slice& data);
-  virtual Status Close();
-  virtual Status Flush();
-  virtual Status Sync();
+  ~TestWritableFile() override;
+  Status Append(const Slice& data) override;
+  Status Close() override;
+  Status Flush() override;
+  Status Sync() override;
 
  private:
   FileState state_;
@@ -128,13 +128,13 @@ class FaultInjectionTestEnv : public EnvWrapper {
  public:
   FaultInjectionTestEnv()
       : EnvWrapper(Env::Default()), filesystem_active_(true) {}
-  virtual ~FaultInjectionTestEnv() {}
-  virtual Status NewWritableFile(const std::string& fname,
-                                 WritableFile** result);
-  virtual Status NewAppendableFile(const std::string& fname,
-                                   WritableFile** result);
-  virtual Status DeleteFile(const std::string& f);
-  virtual Status RenameFile(const std::string& s, const std::string& t);
+  ~FaultInjectionTestEnv() override = default;
+  Status NewWritableFile(const std::string& fname,
+                         WritableFile** result) override;
+  Status NewAppendableFile(const std::string& fname,
+                           WritableFile** result) override;
+  Status DeleteFile(const std::string& f) override;
+  Status RenameFile(const std::string& s, const std::string& t) override;
 
   void WritableFileClosed(const FileState& state);
   Status DropUnsyncedFileData();
@@ -268,10 +268,11 @@ Status FaultInjectionTestEnv::NewAppendableFile(const std::string& fname,
 Status FaultInjectionTestEnv::DropUnsyncedFileData() {
   Status s;
   MutexLock l(&mutex_);
-  for (std::map<std::string, FileState>::const_iterator it =
-           db_file_state_.begin();
-       s.ok() && it != db_file_state_.end(); ++it) {
-    const FileState& state = it->second;
+  for (const auto& kvp : db_file_state_) {
+    if (!s.ok()) {
+      break;
+    }
+    const FileState& state = kvp.second;
     if (!state.IsFullySynced()) {
       s = state.DropUnsyncedData();
     }
@@ -340,12 +341,14 @@ Status FaultInjectionTestEnv::DeleteFilesCreatedAfterLastDirSync() {
   std::set<std::string> new_files(new_files_since_last_dir_sync_.begin(),
                                   new_files_since_last_dir_sync_.end());
   mutex_.Unlock();
-  Status s;
-  std::set<std::string>::const_iterator it;
-  for (it = new_files.begin(); s.ok() && it != new_files.end(); ++it) {
-    s = DeleteFile(*it);
+  Status status;
+  for (const auto& new_file : new_files) {
+    Status delete_status = DeleteFile(new_file);
+    if (!delete_status.ok() && status.ok()) {
+      status = std::move(delete_status);
+    }
   }
-  return s;
+  return status;
 }
 
 void FaultInjectionTestEnv::WritableFileClosed(const FileState& state) {
diff --git a/db/log_reader.cc b/db/log_reader.cc
index f472723..b770fee 100644
--- a/db/log_reader.cc
+++ b/db/log_reader.cc
@@ -13,7 +13,7 @@
 namespace leveldb {
 namespace log {
 
-Reader::Reporter::~Reporter() {}
+Reader::Reporter::~Reporter() = default;
 
 Reader::Reader(SequentialFile* file, Reporter* reporter, bool checksum,
                uint64_t initial_offset)
diff --git a/db/log_writer.cc b/db/log_writer.cc
index 5e83f6a..bfb16fb 100644
--- a/db/log_writer.cc
+++ b/db/log_writer.cc
@@ -29,7 +29,7 @@ Writer::Writer(WritableFile* dest, uint64_t dest_length)
   InitTypeCrc(type_crc_);
 }
 
-Writer::~Writer() {}
+Writer::~Writer() = default;
 
 Status Writer::AddRecord(const Slice& slice) {
   const char* ptr = slice.data();
diff --git a/db/memtable.cc b/db/memtable.cc
index c91405c..00931d4 100644
--- a/db/memtable.cc
+++ b/db/memtable.cc
@@ -47,27 +47,28 @@ class MemTableIterator : public Iterator {
  public:
   explicit MemTableIterator(MemTable::Table* table) : iter_(table) {}
 
-  virtual bool Valid() const { return iter_.Valid(); }
-  virtual void Seek(const Slice& k) { iter_.Seek(EncodeKey(&tmp_, k)); }
-  virtual void SeekToFirst() { iter_.SeekToFirst(); }
-  virtual void SeekToLast() { iter_.SeekToLast(); }
-  virtual void Next() { iter_.Next(); }
-  virtual void Prev() { iter_.Prev(); }
-  virtual Slice key() const { return GetLengthPrefixedSlice(iter_.key()); }
-  virtual Slice value() const {
+  MemTableIterator(const MemTableIterator&) = delete;
+  MemTableIterator& operator=(const MemTableIterator&) = delete;
+
+  ~MemTableIterator() override = default;
+
+  bool Valid() const override { return iter_.Valid(); }
+  void Seek(const Slice& k) override { iter_.Seek(EncodeKey(&tmp_, k)); }
+  void SeekToFirst() override { iter_.SeekToFirst(); }
+  void SeekToLast() override { iter_.SeekToLast(); }
+  void Next() override { iter_.Next(); }
+  void Prev() override { iter_.Prev(); }
+  Slice key() const override { return GetLengthPrefixedSlice(iter_.key()); }
+  Slice value() const override {
     Slice key_slice = GetLengthPrefixedSlice(iter_.key());
     return GetLengthPrefixedSlice(key_slice.data() + key_slice.size());
   }
 
-  virtual Status status() const { return Status::OK(); }
+  Status status() const override { return Status::OK(); }
 
  private:
   MemTable::Table::Iterator iter_;
   std::string tmp_;  // For passing to EncodeKey
-
-  // No copying allowed
-  MemTableIterator(const MemTableIterator&);
-  void operator=(const MemTableIterator&);
 };
 
 Iterator* MemTable::NewIterator() { return new MemTableIterator(&table_); }
diff --git a/db/version_edit.cc b/db/version_edit.cc
index 44a4d02..2385e7d 100644
--- a/db/version_edit.cc
+++ b/db/version_edit.cc
@@ -66,11 +66,10 @@ void VersionEdit::EncodeTo(std::string* dst) const {
     PutLengthPrefixedSlice(dst, compact_pointers_[i].second.Encode());
   }
 
-  for (DeletedFileSet::const_iterator iter = deleted_files_.begin();
-       iter != deleted_files_.end(); ++iter) {
+  for (const auto& deleted_file_kvp : deleted_files_) {
     PutVarint32(dst, kDeletedFile);
-    PutVarint32(dst, iter->first);   // level
-    PutVarint64(dst, iter->second);  // file number
+    PutVarint32(dst, deleted_file_kvp.first);   // level
+    PutVarint64(dst, deleted_file_kvp.second);  // file number
   }
 
   for (size_t i = 0; i < new_files_.size(); i++) {
@@ -233,12 +232,11 @@ std::string VersionEdit::DebugString() const {
     r.append(" ");
     r.append(compact_pointers_[i].second.DebugString());
   }
-  for (DeletedFileSet::const_iterator iter = deleted_files_.begin();
-       iter != deleted_files_.end(); ++iter) {
+  for (const auto& deleted_files_kvp : deleted_files_) {
     r.append("\n  DeleteFile: ");
-    AppendNumberTo(&r, iter->first);
+    AppendNumberTo(&r, deleted_files_kvp.first);
     r.append(" ");
-    AppendNumberTo(&r, iter->second);
+    AppendNumberTo(&r, deleted_files_kvp.second);
   }
   for (size_t i = 0; i < new_files_.size(); i++) {
     const FileMetaData& f = new_files_[i].second;
diff --git a/db/version_edit.h b/db/version_edit.h
index 2dadda7..86b2f22 100644
--- a/db/version_edit.h
+++ b/db/version_edit.h
@@ -29,7 +29,7 @@ struct FileMetaData {
 class VersionEdit {
  public:
   VersionEdit() { Clear(); }
-  ~VersionEdit() {}
+  ~VersionEdit() = default;
 
   void Clear();
 
diff --git a/db/version_set.cc b/db/version_set.cc
index 96a92cc..099fa57 100644
--- a/db/version_set.cc
+++ b/db/version_set.cc
@@ -656,11 +656,9 @@ class VersionSet::Builder {
     }
 
     // Delete files
-    const VersionEdit::DeletedFileSet& del = edit->deleted_files_;
-    for (VersionEdit::DeletedFileSet::const_iterator iter = del.begin();
-         iter != del.end(); ++iter) {
-      const int level = iter->first;
-      const uint64_t number = iter->second;
+    for (const auto& deleted_file_set_kvp : edit->deleted_files_) {
+      const int level = deleted_file_set_kvp.first;
+      const uint64_t number = deleted_file_set_kvp.second;
       levels_[level].deleted_files.insert(number);
     }
 
@@ -701,18 +699,17 @@ class VersionSet::Builder {
       const std::vector<FileMetaData*>& base_files = base_->files_[level];
       std::vector<FileMetaData*>::const_iterator base_iter = base_files.begin();
       std::vector<FileMetaData*>::const_iterator base_end = base_files.end();
-      const FileSet* added = levels_[level].added_files;
-      v->files_[level].reserve(base_files.size() + added->size());
-      for (FileSet::const_iterator added_iter = added->begin();
-           added_iter != added->end(); ++added_iter) {
+      const FileSet* added_files = levels_[level].added_files;
+      v->files_[level].reserve(base_files.size() + added_files->size());
+      for (const auto& added_file : *added_files) {
         // Add all smaller files listed in base_
         for (std::vector<FileMetaData*>::const_iterator bpos =
-                 std::upper_bound(base_iter, base_end, *added_iter, cmp);
+                 std::upper_bound(base_iter, base_end, added_file, cmp);
              base_iter != bpos; ++base_iter) {
           MaybeAddFile(v, level, *base_iter);
         }
 
-        MaybeAddFile(v, level, *added_iter);
+        MaybeAddFile(v, level, added_file);
       }
 
       // Add remaining base files
diff --git a/db/version_set_test.cc b/db/version_set_test.cc
index f7efe2b..c1056a1 100644
--- a/db/version_set_test.cc
+++ b/db/version_set_test.cc
@@ -184,14 +184,14 @@ class AddBoundaryInputsTest {
   std::vector<FileMetaData*> all_files_;
   InternalKeyComparator icmp_;
 
-  AddBoundaryInputsTest() : icmp_(BytewiseComparator()){};
+  AddBoundaryInputsTest() : icmp_(BytewiseComparator()) {}
 
   ~AddBoundaryInputsTest() {
     for (size_t i = 0; i < all_files_.size(); ++i) {
       delete all_files_[i];
     }
     all_files_.clear();
-  };
+  }
 
   FileMetaData* CreateFileMetaData(uint64_t number, InternalKey smallest,
                                    InternalKey largest) {
diff --git a/db/write_batch.cc b/db/write_batch.cc
index 2dec642..b54313c 100644
--- a/db/write_batch.cc
+++ b/db/write_batch.cc
@@ -28,9 +28,9 @@ static const size_t kHeader = 12;
 
 WriteBatch::WriteBatch() { Clear(); }
 
-WriteBatch::~WriteBatch() {}
+WriteBatch::~WriteBatch() = default;
 
-WriteBatch::Handler::~Handler() {}
+WriteBatch::Handler::~Handler() = default;
 
 void WriteBatch::Clear() {
   rep_.clear();
@@ -118,11 +118,11 @@ class MemTableInserter : public WriteBatch::Handler {
   SequenceNumber sequence_;
   MemTable* mem_;
 
-  virtual void Put(const Slice& key, const Slice& value) {
+  void Put(const Slice& key, const Slice& value) override {
     mem_->Add(sequence_, kTypeValue, key, value);
     sequence_++;
   }
-  virtual void Delete(const Slice& key) {
+  void Delete(const Slice& key) override {
     mem_->Add(sequence_, kTypeDeletion, key, Slice());
     sequence_++;
   }
diff --git a/helpers/memenv/memenv.cc b/helpers/memenv/memenv.cc
index b6b790c..2d4fbaa 100644
--- a/helpers/memenv/memenv.cc
+++ b/helpers/memenv/memenv.cc
@@ -223,16 +223,15 @@ class InMemoryEnv : public EnvWrapper {
  public:
   explicit InMemoryEnv(Env* base_env) : EnvWrapper(base_env) {}
 
-  virtual ~InMemoryEnv() {
-    for (FileSystem::iterator i = file_map_.begin(); i != file_map_.end();
-         ++i) {
-      i->second->Unref();
+  ~InMemoryEnv() override {
+    for (const auto& kvp : file_map_) {
+      kvp.second->Unref();
     }
   }
 
   // Partial implementation of the Env interface.
-  virtual Status NewSequentialFile(const std::string& fname,
-                                   SequentialFile** result) {
+  Status NewSequentialFile(const std::string& fname,
+                           SequentialFile** result) override {
     MutexLock lock(&mutex_);
     if (file_map_.find(fname) == file_map_.end()) {
       *result = nullptr;
@@ -243,8 +242,8 @@ class InMemoryEnv : public EnvWrapper {
     return Status::OK();
   }
 
-  virtual Status NewRandomAccessFile(const std::string& fname,
-                                     RandomAccessFile** result) {
+  Status NewRandomAccessFile(const std::string& fname,
+                             RandomAccessFile** result) override {
     MutexLock lock(&mutex_);
     if (file_map_.find(fname) == file_map_.end()) {
       *result = nullptr;
@@ -255,8 +254,8 @@ class InMemoryEnv : public EnvWrapper {
     return Status::OK();
   }
 
-  virtual Status NewWritableFile(const std::string& fname,
-                                 WritableFile** result) {
+  Status NewWritableFile(const std::string& fname,
+                         WritableFile** result) override {
     MutexLock lock(&mutex_);
     FileSystem::iterator it = file_map_.find(fname);
 
@@ -275,8 +274,8 @@ class InMemoryEnv : public EnvWrapper {
     return Status::OK();
   }
 
-  virtual Status NewAppendableFile(const std::string& fname,
-                                   WritableFile** result) {
+  Status NewAppendableFile(const std::string& fname,
+                           WritableFile** result) override {
     MutexLock lock(&mutex_);
     FileState** sptr = &file_map_[fname];
     FileState* file = *sptr;
@@ -288,19 +287,18 @@ class InMemoryEnv : public EnvWrapper {
     return Status::OK();
   }
 
-  virtual bool FileExists(const std::string& fname) {
+  bool FileExists(const std::string& fname) override {
     MutexLock lock(&mutex_);
     return file_map_.find(fname) != file_map_.end();
   }
 
-  virtual Status GetChildren(const std::string& dir,
-                             std::vector<std::string>* result) {
+  Status GetChildren(const std::string& dir,
+                     std::vector<std::string>* result) override {
     MutexLock lock(&mutex_);
     result->clear();
 
-    for (FileSystem::iterator i = file_map_.begin(); i != file_map_.end();
-         ++i) {
-      const std::string& filename = i->first;
+    for (const auto& kvp : file_map_) {
+      const std::string& filename = kvp.first;
 
       if (filename.size() >= dir.size() + 1 && filename[dir.size()] == '/' &&
           Slice(filename).starts_with(Slice(dir))) {
@@ -321,7 +319,7 @@ class InMemoryEnv : public EnvWrapper {
     file_map_.erase(fname);
   }
 
-  virtual Status DeleteFile(const std::string& fname) {
+  Status DeleteFile(const std::string& fname) override {
     MutexLock lock(&mutex_);
     if (file_map_.find(fname) == file_map_.end()) {
       return Status::IOError(fname, "File not found");
@@ -331,11 +329,11 @@ class InMemoryEnv : public EnvWrapper {
     return Status::OK();
   }
 
-  virtual Status CreateDir(const std::string& dirname) { return Status::OK(); }
+  Status CreateDir(const std::string& dirname) override { return Status::OK(); }
 
-  virtual Status DeleteDir(const std::string& dirname) { return Status::OK(); }
+  Status DeleteDir(const std::string& dirname) override { return Status::OK(); }
 
-  virtual Status GetFileSize(const std::string& fname, uint64_t* file_size) {
+  Status GetFileSize(const std::string& fname, uint64_t* file_size) override {
     MutexLock lock(&mutex_);
     if (file_map_.find(fname) == file_map_.end()) {
       return Status::IOError(fname, "File not found");
@@ -345,7 +343,8 @@ class InMemoryEnv : public EnvWrapper {
     return Status::OK();
   }
 
-  virtual Status RenameFile(const std::string& src, const std::string& target) {
+  Status RenameFile(const std::string& src,
+                    const std::string& target) override {
     MutexLock lock(&mutex_);
     if (file_map_.find(src) == file_map_.end()) {
       return Status::IOError(src, "File not found");
@@ -357,22 +356,22 @@ class InMemoryEnv : public EnvWrapper {
     return Status::OK();
   }
 
-  virtual Status LockFile(const std::string& fname, FileLock** lock) {
+  Status LockFile(const std::string& fname, FileLock** lock) override {
     *lock = new FileLock;
     return Status::OK();
   }
 
-  virtual Status UnlockFile(FileLock* lock) {
+  Status UnlockFile(FileLock* lock) override {
     delete lock;
     return Status::OK();
   }
 
-  virtual Status GetTestDirectory(std::string* path) {
+  Status GetTestDirectory(std::string* path) override {
     *path = "/test";
     return Status::OK();
   }
 
-  virtual Status NewLogger(const std::string& fname, Logger** result) {
+  Status NewLogger(const std::string& fname, Logger** result) override {
     *result = new NoOpLogger;
     return Status::OK();
   }
diff --git a/include/leveldb/db.h b/include/leveldb/db.h
index ea3d9e5..b73014a 100644
--- a/include/leveldb/db.h
+++ b/include/leveldb/db.h
@@ -33,7 +33,7 @@ class LEVELDB_EXPORT Snapshot {
 
 // A range of keys
 struct LEVELDB_EXPORT Range {
-  Range() {}
+  Range() = default;
   Range(const Slice& s, const Slice& l) : start(s), limit(l) {}
 
   Slice start;  // Included in the range
diff --git a/table/format.h b/table/format.h
index 2ad145c..e49dfdc 100644
--- a/table/format.h
+++ b/table/format.h
@@ -53,7 +53,7 @@ class Footer {
   // of two block handles and a magic number.
   enum { kEncodedLength = 2 * BlockHandle::kMaxEncodedLength + 8 };
 
-  Footer() {}
+  Footer() = default;
 
   // The block handle for the metaindex block of the table
   const BlockHandle& metaindex_handle() const { return metaindex_handle_; }
diff --git a/table/table_test.cc b/table/table_test.cc
index 0974052..3c63e32 100644
--- a/table/table_test.cc
+++ b/table/table_test.cc
@@ -89,7 +89,7 @@ struct STLLessThan {
 
 class StringSink : public WritableFile {
  public:
-  ~StringSink() {}
+  ~StringSink() = default;
 
   const std::string& contents() const { return contents_; }
 
@@ -111,7 +111,7 @@ class StringSource : public RandomAccessFile {
   StringSource(const Slice& contents)
       : contents_(contents.data(), contents.size()) {}
 
-  virtual ~StringSource() {}
+  virtual ~StringSource() = default;
 
   uint64_t Size() const { return contents_.size(); }
 
@@ -139,7 +139,7 @@ typedef std::map<std::string, std::string, STLLessThan> KVMap;
 class Constructor {
  public:
   explicit Constructor(const Comparator* cmp) : data_(STLLessThan(cmp)) {}
-  virtual ~Constructor() {}
+  virtual ~Constructor() = default;
 
   void Add(const std::string& key, const Slice& value) {
     data_[key] = value.ToString();
@@ -152,8 +152,8 @@ class Constructor {
               KVMap* kvmap) {
     *kvmap = data_;
     keys->clear();
-    for (KVMap::const_iterator it = data_.begin(); it != data_.end(); ++it) {
-      keys->push_back(it->first);
+    for (const auto& kvp : data_) {
+      keys->push_back(kvp.first);
     }
     data_.clear();
     Status s = FinishImpl(options, *kvmap);
@@ -165,7 +165,7 @@ class Constructor {
 
   virtual Iterator* NewIterator() const = 0;
 
-  virtual const KVMap& data() { return data_; }
+  const KVMap& data() const { return data_; }
 
   virtual DB* db() const { return nullptr; }  // Overridden in DBConstructor
 
@@ -177,14 +177,14 @@ class BlockConstructor : public Constructor {
  public:
   explicit BlockConstructor(const Comparator* cmp)
       : Constructor(cmp), comparator_(cmp), block_(nullptr) {}
-  ~BlockConstructor() { delete block_; }
-  virtual Status FinishImpl(const Options& options, const KVMap& data) {
+  ~BlockConstructor() override { delete block_; }
+  Status FinishImpl(const Options& options, const KVMap& data) override {
     delete block_;
     block_ = nullptr;
     BlockBuilder builder(&options);
 
-    for (KVMap::const_iterator it = data.begin(); it != data.end(); ++it) {
-      builder.Add(it->first, it->second);
+    for (const auto& kvp : data) {
+      builder.Add(kvp.first, kvp.second);
     }
     // Open the block
     data_ = builder.Finish().ToString();
@@ -195,12 +195,12 @@ class BlockConstructor : public Constructor {
     block_ = new Block(contents);
     return Status::OK();
   }
-  virtual Iterator* NewIterator() const {
+  Iterator* NewIterator() const override {
     return block_->NewIterator(comparator_);
   }
 
  private:
-  const Comparator* comparator_;
+  const Comparator* const comparator_;
   std::string data_;
   Block* block_;
 
@@ -211,14 +211,14 @@ class TableConstructor : public Constructor {
  public:
   TableConstructor(const Comparator* cmp)
       : Constructor(cmp), source_(nullptr), table_(nullptr) {}
-  ~TableConstructor() { Reset(); }
-  virtual Status FinishImpl(const Options& options, const KVMap& data) {
+  ~TableConstructor() override { Reset(); }
+  Status FinishImpl(const Options& options, const KVMap& data) override {
     Reset();
     StringSink sink;
     TableBuilder builder(options, &sink);
 
-    for (KVMap::const_iterator it = data.begin(); it != data.end(); ++it) {
-      builder.Add(it->first, it->second);
+    for (const auto& kvp : data) {
+      builder.Add(kvp.first, kvp.second);
       ASSERT_TRUE(builder.status().ok());
     }
     Status s = builder.Finish();
@@ -233,7 +233,7 @@ class TableConstructor : public Constructor {
     return Table::Open(table_options, source_, sink.contents().size(), &table_);
   }
 
-  virtual Iterator* NewIterator() const {
+  Iterator* NewIterator() const override {
     return table_->NewIterator(ReadOptions());
   }
 
@@ -259,20 +259,25 @@ class TableConstructor : public Constructor {
 class KeyConvertingIterator : public Iterator {
  public:
   explicit KeyConvertingIterator(Iterator* iter) : iter_(iter) {}
-  virtual ~KeyConvertingIterator() { delete iter_; }
-  virtual bool Valid() const { return iter_->Valid(); }
-  virtual void Seek(const Slice& target) {
+
+  KeyConvertingIterator(const KeyConvertingIterator&) = delete;
+  KeyConvertingIterator& operator=(const KeyConvertingIterator&) = delete;
+
+  ~KeyConvertingIterator() override { delete iter_; }
+
+  bool Valid() const override { return iter_->Valid(); }
+  void Seek(const Slice& target) override {
     ParsedInternalKey ikey(target, kMaxSequenceNumber, kTypeValue);
     std::string encoded;
     AppendInternalKey(&encoded, ikey);
     iter_->Seek(encoded);
   }
-  virtual void SeekToFirst() { iter_->SeekToFirst(); }
-  virtual void SeekToLast() { iter_->SeekToLast(); }
-  virtual void Next() { iter_->Next(); }
-  virtual void Prev() { iter_->Prev(); }
+  void SeekToFirst() override { iter_->SeekToFirst(); }
+  void SeekToLast() override { iter_->SeekToLast(); }
+  void Next() override { iter_->Next(); }
+  void Prev() override { iter_->Prev(); }
 
-  virtual Slice key() const {
+  Slice key() const override {
     assert(Valid());
     ParsedInternalKey key;
     if (!ParseInternalKey(iter_->key(), &key)) {
@@ -282,18 +287,14 @@ class KeyConvertingIterator : public Iterator {
     return key.user_key;
   }
 
-  virtual Slice value() const { return iter_->value(); }
-  virtual Status status() const {
+  Slice value() const override { return iter_->value(); }
+  Status status() const override {
     return status_.ok() ? iter_->status() : status_;
   }
 
  private:
   mutable Status status_;
   Iterator* iter_;
-
-  // No copying allowed
-  KeyConvertingIterator(const KeyConvertingIterator&);
-  void operator=(const KeyConvertingIterator&);
 };
 
 class MemTableConstructor : public Constructor {
@@ -303,24 +304,24 @@ class MemTableConstructor : public Constructor {
     memtable_ = new MemTable(internal_comparator_);
     memtable_->Ref();
   }
-  ~MemTableConstructor() { memtable_->Unref(); }
-  virtual Status FinishImpl(const Options& options, const KVMap& data) {
+  ~MemTableConstructor() override { memtable_->Unref(); }
+  Status FinishImpl(const Options& options, const KVMap& data) override {
     memtable_->Unref();
     memtable_ = new MemTable(internal_comparator_);
     memtable_->Ref();
     int seq = 1;
-    for (KVMap::const_iterator it = data.begin(); it != data.end(); ++it) {
-      memtable_->Add(seq, kTypeValue, it->first, it->second);
+    for (const auto& kvp : data) {
+      memtable_->Add(seq, kTypeValue, kvp.first, kvp.second);
       seq++;
     }
     return Status::OK();
   }
-  virtual Iterator* NewIterator() const {
+  Iterator* NewIterator() const override {
     return new KeyConvertingIterator(memtable_->NewIterator());
   }
 
  private:
-  InternalKeyComparator internal_comparator_;
+  const InternalKeyComparator internal_comparator_;
   MemTable* memtable_;
 };
 
@@ -331,23 +332,23 @@ class DBConstructor : public Constructor {
     db_ = nullptr;
     NewDB();
   }
-  ~DBConstructor() { delete db_; }
-  virtual Status FinishImpl(const Options& options, const KVMap& data) {
+  ~DBConstructor() override { delete db_; }
+  Status FinishImpl(const Options& options, const KVMap& data) override {
     delete db_;
     db_ = nullptr;
     NewDB();
-    for (KVMap::const_iterator it = data.begin(); it != data.end(); ++it) {
+    for (const auto& kvp : data) {
       WriteBatch batch;
-      batch.Put(it->first, it->second);
+      batch.Put(kvp.first, kvp.second);
       ASSERT_TRUE(db_->Write(WriteOptions(), &batch).ok());
     }
     return Status::OK();
   }
-  virtual Iterator* NewIterator() const {
+  Iterator* NewIterator() const override {
     return db_->NewIterator(ReadOptions());
   }
 
-  virtual DB* db() const { return db_; }
+  DB* db() const override { return db_; }
 
  private:
   void NewDB() {
@@ -365,7 +366,7 @@ class DBConstructor : public Constructor {
     ASSERT_TRUE(status.ok()) << status.ToString();
   }
 
-  const Comparator* comparator_;
+  const Comparator* const comparator_;
   DB* db_;
 };
 
diff --git a/table/two_level_iterator.cc b/table/two_level_iterator.cc
index 5340a4d..1fc4626 100644
--- a/table/two_level_iterator.cc
+++ b/table/two_level_iterator.cc
@@ -77,7 +77,7 @@ TwoLevelIterator::TwoLevelIterator(Iterator* index_iter,
       index_iter_(index_iter),
       data_iter_(nullptr) {}
 
-TwoLevelIterator::~TwoLevelIterator() {}
+TwoLevelIterator::~TwoLevelIterator() = default;
 
 void TwoLevelIterator::Seek(const Slice& target) {
   index_iter_.Seek(target);
diff --git a/util/comparator.cc b/util/comparator.cc
index 26d1eb3..c5766e9 100644
--- a/util/comparator.cc
+++ b/util/comparator.cc
@@ -2,32 +2,34 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
+#include "leveldb/comparator.h"
+
 #include <algorithm>
 #include <cstdint>
 #include <string>
+#include <type_traits>
 
-#include "leveldb/comparator.h"
 #include "leveldb/slice.h"
 #include "util/logging.h"
 #include "util/no_destructor.h"
 
 namespace leveldb {
 
-Comparator::~Comparator() {}
+Comparator::~Comparator() = default;
 
 namespace {
 class BytewiseComparatorImpl : public Comparator {
  public:
-  BytewiseComparatorImpl() {}
+  BytewiseComparatorImpl() = default;
 
-  virtual const char* Name() const { return "leveldb.BytewiseComparator"; }
+  const char* Name() const override { return "leveldb.BytewiseComparator"; }
 
-  virtual int Compare(const Slice& a, const Slice& b) const {
+  int Compare(const Slice& a, const Slice& b) const override {
     return a.compare(b);
   }
 
-  virtual void FindShortestSeparator(std::string* start,
-                                     const Slice& limit) const {
+  void FindShortestSeparator(std::string* start,
+                             const Slice& limit) const override {
     // Find length of common prefix
     size_t min_length = std::min(start->size(), limit.size());
     size_t diff_index = 0;
@@ -49,7 +51,7 @@ class BytewiseComparatorImpl : public Comparator {
     }
   }
 
-  virtual void FindShortSuccessor(std::string* key) const {
+  void FindShortSuccessor(std::string* key) const override {
     // Find first character that can be incremented
     size_t n = key->size();
     for (size_t i = 0; i < n; i++) {
diff --git a/util/env.cc b/util/env.cc
index 6cd5f2e..d2f0aef 100644
--- a/util/env.cc
+++ b/util/env.cc
@@ -6,21 +6,21 @@
 
 namespace leveldb {
 
-Env::~Env() {}
+Env::~Env() = default;
 
 Status Env::NewAppendableFile(const std::string& fname, WritableFile** result) {
   return Status::NotSupported("NewAppendableFile", fname);
 }
 
-SequentialFile::~SequentialFile() {}
+SequentialFile::~SequentialFile() = default;
 
-RandomAccessFile::~RandomAccessFile() {}
+RandomAccessFile::~RandomAccessFile() = default;
 
-WritableFile::~WritableFile() {}
+WritableFile::~WritableFile() = default;
 
-Logger::~Logger() {}
+Logger::~Logger() = default;
 
-FileLock::~FileLock() {}
+FileLock::~FileLock() = default;
 
 void Log(Logger* info_log, const char* format, ...) {
   if (info_log != nullptr) {