8 files changed, 467 insertions, 39 deletions

diff --git a/include/cru/common/Base.hpp b/include/cru/common/Base.hpp
index a5a9421d..560f83bb 100644
--- a/include/cru/common/Base.hpp
+++ b/include/cru/common/Base.hpp
@@ -1,8 +1,8 @@
 #pragma once
 #include "PreConfig.hpp"
 
+#include <exception>
 #include <gsl/gsl>
-
 #include <stdexcept>
 
 #define CRU_UNUSED(entity) static_cast<void>(entity);
@@ -42,12 +42,17 @@ struct Interface {
   virtual ~Interface() = default;
 };
 
-[[noreturn]] inline void UnreachableCode() {
-  throw std::runtime_error("Unreachable code.");
-}
+[[noreturn]] inline void UnreachableCode() { std::terminate(); }
 
 using Index = gsl::index;
 
+// https://www.boost.org/doc/libs/1_54_0/doc/html/hash/reference.html#boost.hash_combine
+template <class T>
+inline void hash_combine(std::size_t& s, const T& v) {
+  std::hash<T> h;
+  s ^= h(v) + 0x9e3779b9 + (s << 6) + (s >> 2);
+}
+
 #define CRU_DEFINE_CLASS_LOG_TAG(tag) \
  private:                             \
   constexpr static std::u16string_view log_tag = tag;
diff --git a/include/cru/common/ClonablePtr.hpp b/include/cru/common/ClonablePtr.hpp
new file mode 100644
index 00000000..5e4b80c9
--- /dev/null
+++ b/include/cru/common/ClonablePtr.hpp
@@ -0,0 +1,204 @@
+#pragma once
+
+#include <cstddef>
+#include <functional>
+#include <memory>
+#include <type_traits>
+
+namespace cru {
+template <typename TClonable>
+class ClonablePtr {
+  template <typename T>
+  friend class ClonablePtr;
+
+ public:
+  using element_type = typename std::unique_ptr<TClonable>::element_type;
+  using pointer = typename std::unique_ptr<TClonable>::pointer;
+
+  ClonablePtr() = default;
+  ClonablePtr(std::nullptr_t) noexcept : ptr_(nullptr) {}
+  explicit ClonablePtr(pointer p) noexcept : ptr_(p) {}
+  ClonablePtr(std::unique_ptr<element_type>&& p) noexcept
+      : ptr_(std::move(p)) {}
+  template <typename O,
+            std::enable_if_t<std::is_convertible_v<
+                                 typename ClonablePtr<O>::pointer, pointer>,
+                             int> = 0>
+  ClonablePtr(std::unique_ptr<O>&& p) : ptr_(std::move(p)) {}
+  ClonablePtr(const ClonablePtr& other) : ptr_(other.ptr_->Clone()) {}
+  ClonablePtr(ClonablePtr&& other) = default;
+  template <typename O,
+            std::enable_if_t<std::is_convertible_v<
+                                 typename ClonablePtr<O>::pointer, pointer>,
+                             int> = 0>
+  ClonablePtr(const ClonablePtr<O>& other) : ptr_(other.ptr_->Clone()) {}
+  template <typename O,
+            std::enable_if_t<std::is_convertible_v<
+                                 typename ClonablePtr<O>::pointer, pointer>,
+                             int> = 0>
+  ClonablePtr(ClonablePtr<O>&& other) noexcept : ptr_(std::move(other.ptr_)) {}
+  ClonablePtr& operator=(std::nullptr_t) noexcept {
+    ptr_ = nullptr;
+    return *this;
+  }
+  ClonablePtr& operator=(std::unique_ptr<element_type>&& other) noexcept {
+    ptr_ = std::move(other);
+    return *this;
+  }
+  template <typename O,
+            std::enable_if_t<std::is_convertible_v<
+                                 typename ClonablePtr<O>::pointer, pointer>,
+                             int> = 0>
+  ClonablePtr& operator=(std::unique_ptr<O>&& p) noexcept {
+    ptr_ = std::move(p);
+    return *this;
+  }
+  ClonablePtr& operator=(const ClonablePtr& other) {
+    if (this != &other) {
+      ptr_ = std::unique_ptr<element_type>(other.ptr_->Clone());
+    }
+    return *this;
+  }
+  ClonablePtr& operator=(ClonablePtr&& other) = default;
+  template <typename O,
+            std::enable_if_t<std::is_convertible_v<
+                                 typename ClonablePtr<O>::pointer, pointer>,
+                             int> = 0>
+  ClonablePtr& operator=(const ClonablePtr<O>& other) noexcept {
+    if (this != &other) {
+      ptr_ = std::unique_ptr<element_type>(other.ptr_->Clone());
+    }
+    return *this;
+  }
+  template <typename O,
+            std::enable_if_t<std::is_convertible_v<
+                                 typename ClonablePtr<O>::pointer, pointer>,
+                             int> = 0>
+  ClonablePtr& operator=(ClonablePtr<O>&& other) noexcept {
+    ptr_ = std::move(other.ptr_);
+  }
+
+  ~ClonablePtr() = default;
+
+ public:
+  pointer release() noexcept { return ptr_.release(); }
+  void reset(pointer p = pointer()) noexcept { ptr_.reset(p); }
+  void swap(ClonablePtr& other) noexcept { ptr_.swap(other.ptr_); }
+
+ public:
+  pointer get() const noexcept { return ptr_.get(); }
+
+  operator bool() const noexcept { return ptr_; }
+
+  element_type& operator*() const noexcept { return *ptr_; }
+  pointer operator->() const noexcept { return ptr_.get(); }
+
+ private:
+  std::unique_ptr<element_type> ptr_;
+};
+
+template <typename T>
+void swap(ClonablePtr<T>& left, ClonablePtr<T>& right) noexcept {
+  left.swap(right);
+}
+
+template <typename T>
+bool operator==(const ClonablePtr<T>& left, const ClonablePtr<T>& right) {
+  return left.get() == right.get();
+}
+
+template <typename T>
+bool operator!=(const ClonablePtr<T>& left, const ClonablePtr<T>& right) {
+  return left.get() != right.get();
+}
+
+template <typename T>
+bool operator<(const ClonablePtr<T>& left, const ClonablePtr<T>& right) {
+  return left.get() < right.get();
+}
+
+template <typename T>
+bool operator<=(const ClonablePtr<T>& left, const ClonablePtr<T>& right) {
+  return left.get() <= right.get();
+}
+
+template <typename T>
+bool operator>(const ClonablePtr<T>& left, const ClonablePtr<T>& right) {
+  return left.get() > right.get();
+}
+
+template <typename T>
+bool operator>=(const ClonablePtr<T>& left, const ClonablePtr<T>& right) {
+  return left.get() >= right.get();
+}
+
+template <typename T>
+bool operator==(const ClonablePtr<T>& left, std::nullptr_t) {
+  return left.get() == nullptr;
+}
+
+template <typename T>
+bool operator!=(const ClonablePtr<T>& left, std::nullptr_t) {
+  return left.get() != nullptr;
+}
+
+template <typename T>
+bool operator<(const ClonablePtr<T>& left, std::nullptr_t) {
+  return left.get() < nullptr;
+}
+
+template <typename T>
+bool operator<=(const ClonablePtr<T>& left, std::nullptr_t) {
+  return left.get() <= nullptr;
+}
+
+template <typename T>
+bool operator>(const ClonablePtr<T>& left, std::nullptr_t) {
+  return left.get() > nullptr;
+}
+
+template <typename T>
+bool operator>=(const ClonablePtr<T>& left, std::nullptr_t) {
+  return left.get() >= nullptr;
+}
+
+template <typename T>
+bool operator==(std::nullptr_t, const ClonablePtr<T>& right) {
+  return nullptr == right.get();
+}
+
+template <typename T>
+bool operator!=(std::nullptr_t, const ClonablePtr<T>& right) {
+  return nullptr != right.get();
+}
+
+template <typename T>
+bool operator<(std::nullptr_t, const ClonablePtr<T>& right) {
+  return nullptr < right.get();
+}
+
+template <typename T>
+bool operator<=(std::nullptr_t, const ClonablePtr<T>& right) {
+  return nullptr <= right.get();
+}
+
+template <typename T>
+bool operator>(std::nullptr_t, const ClonablePtr<T>& right) {
+  return nullptr > right.get();
+}
+
+template <typename T>
+bool operator>=(std::nullptr_t, const ClonablePtr<T>& right) {
+  return nullptr >= right.get();
+}
+
+}  // namespace cru
+
+namespace std {
+template <typename T>
+struct hash<cru::ClonablePtr<T>> {
+  std::size_t operator()(const cru::ClonablePtr<T>& p) const {
+    return std::hash<typename cru::ClonablePtr<T>::pointer>(p.get());
+  }
+};
+}  // namespace std
diff --git a/include/cru/common/Event.hpp b/include/cru/common/Event.hpp
index 377ca7f3..b6999aa4 100644
--- a/include/cru/common/Event.hpp
+++ b/include/cru/common/Event.hpp
@@ -5,14 +5,19 @@
 
 #include <algorithm>
 #include <functional>
+#include <initializer_list>
 #include <memory>
 #include <utility>
+#include <variant>
 #include <vector>
 
 namespace cru {
 class EventRevoker;
 
 namespace details {
+template <class>
+inline constexpr bool always_false_v = false;
+
 // Base class of all Event<T...>.
 // It erases event args types and provides a
 // unified form to create event revoker and
@@ -24,10 +29,8 @@ class EventBase : public SelfResolvable<EventBase> {
   using EventHandlerToken = long;
 
   EventBase() {}
-  EventBase(const EventBase& other) = delete;
-  EventBase(EventBase&& other) = delete;
-  EventBase& operator=(const EventBase& other) = delete;
-  EventBase& operator=(EventBase&& other) = delete;
+  CRU_DELETE_COPY(EventBase)
+  CRU_DEFAULT_MOVE(EventBase)
   virtual ~EventBase() = default;
 
   // Remove the handler with the given token. If the token
@@ -84,78 +87,114 @@ using DeducedEventArgs = std::conditional_t<
     std::is_lvalue_reference_v<TRaw>, TRaw,
     std::conditional_t<std::is_scalar_v<TRaw>, TRaw, const TRaw&>>;
 
+struct IBaseEvent {
+ protected:
+  IBaseEvent() = default;
+  CRU_DELETE_COPY(IBaseEvent)
+  CRU_DEFAULT_MOVE(IBaseEvent)
+  ~IBaseEvent() = default;  // Note that user can't destroy a Event via IEvent.
+                            // So destructor should be protected.
+
+  using SpyOnlyHandler = std::function<void()>;
+
+ public:
+  virtual EventRevoker AddSpyOnlyHandler(SpyOnlyHandler handler) = 0;
+};
+
 // Provides an interface of event.
 // IEvent only allow to add handler but not to raise the event. You may
 // want to create an Event object and expose IEvent only so users won't
 // be able to emit the event.
 template <typename TEventArgs>
-struct IEvent {
+struct IEvent : virtual IBaseEvent {
  public:
   using EventArgs = DeducedEventArgs<TEventArgs>;
   using EventHandler = std::function<void(EventArgs)>;
+  using ShortCircuitHandler = std::function<bool(EventArgs)>;
 
  protected:
   IEvent() = default;
-  IEvent(const IEvent& other) = delete;
-  IEvent(IEvent&& other) = delete;
-  IEvent& operator=(const IEvent& other) = delete;
-  IEvent& operator=(IEvent&& other) = delete;
+  CRU_DELETE_COPY(IEvent)
+  CRU_DEFAULT_MOVE(IEvent)
   ~IEvent() = default;  // Note that user can't destroy a Event via IEvent. So
                         // destructor should be protected.
 
  public:
-  virtual EventRevoker AddHandler(const EventHandler& handler) = 0;
-  virtual EventRevoker AddHandler(EventHandler&& handler) = 0;
+  virtual EventRevoker AddHandler(EventHandler handler) = 0;
+  virtual EventRevoker AddShortCircuitHandler(ShortCircuitHandler handler) = 0;
+  virtual EventRevoker PrependShortCircuitHandler(
+      ShortCircuitHandler handler) = 0;
 };
 
 // A non-copyable non-movable Event class.
 // It stores a list of event handlers.
 template <typename TEventArgs>
 class Event : public details::EventBase, public IEvent<TEventArgs> {
+  using typename IEvent<TEventArgs>::EventArgs;
+
+  using typename IBaseEvent::SpyOnlyHandler;
   using typename IEvent<TEventArgs>::EventHandler;
+  using typename IEvent<TEventArgs>::ShortCircuitHandler;
 
  private:
   struct HandlerData {
-    HandlerData(EventHandlerToken token, EventHandler handler)
-        : token(token), handler(handler) {}
+    HandlerData(EventHandlerToken token, ShortCircuitHandler handler)
+        : token(token), handler(std::move(handler)) {}
     EventHandlerToken token;
-    EventHandler handler;
+    ShortCircuitHandler handler;
   };
 
  public:
   Event() = default;
-  Event(const Event&) = delete;
-  Event& operator=(const Event&) = delete;
-  Event(Event&&) = delete;
-  Event& operator=(Event&&) = delete;
+  CRU_DELETE_COPY(Event)
+  CRU_DEFAULT_MOVE(Event)
   ~Event() = default;
 
-  EventRevoker AddHandler(const EventHandler& handler) override {
+  EventRevoker AddSpyOnlyHandler(SpyOnlyHandler handler) override {
+    return AddShortCircuitHandler([handler = std::move(handler)](EventArgs) {
+      handler();
+      return false;
+    });
+  }
+
+  EventRevoker AddHandler(EventHandler handler) override {
+    return AddShortCircuitHandler(
+        [handler = std::move(handler)](EventArgs args) {
+          handler(args);
+          return false;
+        });
+  }
+
+  // Handler return true to short circuit following handlers.
+  EventRevoker AddShortCircuitHandler(ShortCircuitHandler handler) override {
     const auto token = current_token_++;
-    this->handler_data_list_.emplace_back(token, handler);
+    this->handler_data_list_.emplace_back(token, std::move(handler));
     return CreateRevoker(token);
   }
 
-  EventRevoker AddHandler(EventHandler&& handler) override {
+  // Handler return true to short circuit following handlers.
+  EventRevoker PrependShortCircuitHandler(
+      ShortCircuitHandler handler) override {
     const auto token = current_token_++;
-    this->handler_data_list_.emplace_back(token, std::move(handler));
+    this->handler_data_list_.emplace(this->handler_data_list_.cbegin(), token,
+                                     std::move(handler));
     return CreateRevoker(token);
   }
 
   // This method will make a copy of all handlers. Because user might delete a
-  // handler in a handler, which may lead to seg fault as the handler is deleted
-  // while being executed.
-  // Thanks to this behavior, all handlers will be taken a snapshot when Raise
-  // is called, so even if you delete a handler during this period, all handlers
-  // in the snapshot will be executed.
-  void Raise(typename IEvent<TEventArgs>::EventArgs args) {
-    std::vector<EventHandler> handlers;
+  // handler in a handler, which may lead to seg fault as the handler is
+  // deleted while being executed. Thanks to this behavior, all handlers will
+  // be taken a snapshot when Raise is called, so even if you delete a handler
+  // during this period, all handlers in the snapshot will be executed.
+  void Raise(EventArgs args) {
+    std::vector<ShortCircuitHandler> handlers;
     handlers.reserve(this->handler_data_list_.size());
     for (const auto& data : this->handler_data_list_) {
       handlers.push_back(data.handler);
     }
     for (const auto& handler : handlers) {
-      handler(args);
+      auto short_circuit = handler(args);
+      if (short_circuit) return;
     }
   }
 
@@ -183,6 +222,7 @@ struct EventRevokerDestroyer {
 };
 }  // namespace details
 
+// A guard class for event revoker. Automatically revoke it when destroyed.
 class EventRevokerGuard {
  public:
   EventRevokerGuard() = default;
@@ -201,7 +241,9 @@ class EventRevokerGuard {
     return *revoker_;
   }
 
-  void Release() { revoker_.release(); }
+  EventRevoker Release() { return std::move(*revoker_.release()); }
+
+  void Reset() { revoker_.reset(); }
 
   void Reset(EventRevoker&& revoker) {
     revoker_.reset(new EventRevoker(std::move(revoker)));
@@ -209,5 +251,32 @@ class EventRevokerGuard {
 
  private:
   std::unique_ptr<EventRevoker, details::EventRevokerDestroyer> revoker_;
-};  // namespace cru
+};
+
+class EventRevokerListGuard {
+ public:
+  EventRevokerListGuard() = default;
+  EventRevokerListGuard(const EventRevokerListGuard& other) = delete;
+  EventRevokerListGuard(EventRevokerListGuard&& other) = default;
+  EventRevokerListGuard& operator=(const EventRevokerListGuard& other) = delete;
+  EventRevokerListGuard& operator=(EventRevokerListGuard&& other) = default;
+  ~EventRevokerListGuard() = default;
+
+ public:
+  void Add(EventRevoker&& revoker) {
+    event_revoker_guard_list_.push_back(EventRevokerGuard(std::move(revoker)));
+  }
+
+  EventRevokerListGuard& operator+=(EventRevoker&& revoker) {
+    this->Add(std::move(revoker));
+    return *this;
+  }
+
+  void Clear() { event_revoker_guard_list_.clear(); }
+
+  bool IsEmpty() const { return event_revoker_guard_list_.empty(); }
+
+ private:
+  std::vector<EventRevokerGuard> event_revoker_guard_list_;
+};
 }  // namespace cru
diff --git a/include/cru/common/Format.hpp b/include/cru/common/Format.hpp
new file mode 100644
index 00000000..59f34036
--- /dev/null
+++ b/include/cru/common/Format.hpp
@@ -0,0 +1,23 @@
+#pragma once
+#include "Base.hpp"
+
+#include "StringUtil.hpp"
+
+#include <array>
+#include <charconv>
+#include <string>
+#include <string_view>
+#include <system_error>
+#include <type_traits>
+
+namespace cru {
+template <typename T, typename = std::enable_if_t<std::is_arithmetic_v<T>>>
+std::u16string ToUtf16String(T number) {
+  std::array<char, 40> buffer;
+  auto result =
+      std::to_chars(buffer.data(), buffer.data() + buffer.size(), number);
+  Ensures(result.ec == std::errc());
+  std::string_view utf8_result(buffer.data(), result.ptr - buffer.data());
+  return ToUtf16(utf8_result);
+}
+}  // namespace cru
diff --git a/include/cru/common/HandlerRegistry.hpp b/include/cru/common/HandlerRegistry.hpp
new file mode 100644
index 00000000..bd74a9e0
--- /dev/null
+++ b/include/cru/common/HandlerRegistry.hpp
@@ -0,0 +1,86 @@
+#pragma once
+#include "Base.hpp"
+
+#include <algorithm>
+#include <functional>
+#include <utility>
+#include <vector>
+
+namespace cru {
+
+template <typename T>
+class HandlerRegistryIterator {
+ public:
+  using RawIterator =
+      typename std::vector<std::pair<int, std::function<T>>>::const_iterator;
+
+  explicit HandlerRegistryIterator(RawIterator raw) : raw_(std::move(raw)) {}
+
+  CRU_DELETE_COPY(HandlerRegistryIterator)
+  CRU_DELETE_MOVE(HandlerRegistryIterator)
+
+  ~HandlerRegistryIterator() = default;
+
+  const std::function<T>& operator*() const { return raw_->second; }
+  const std::function<T>* operator->() const { return &raw_->second; }
+
+  HandlerRegistryIterator& operator++() {
+    ++raw_;
+    return *this;
+  }
+
+  HandlerRegistryIterator operator++(int) {
+    auto c = *this;
+    this->operator++();
+    return c;
+  }
+
+  bool operator==(const HandlerRegistryIterator<T>& other) const {
+    return this->raw_ == other.raw_;
+  }
+
+  bool operator!=(const HandlerRegistryIterator<T>& other) const {
+    return !this->operator==(other);
+  }
+
+ private:
+  RawIterator raw_;
+};
+
+template <typename T>
+class HandlerRegistry final {
+ public:
+  HandlerRegistry() = default;
+  CRU_DEFAULT_COPY(HandlerRegistry)
+  CRU_DEFAULT_MOVE(HandlerRegistry)
+  ~HandlerRegistry() = default;
+
+ public:
+  int AddHandler(std::function<T> handler) {
+    auto id = current_id_++;
+    handler_list_.push_back({id, std::move(handler)});
+  }
+
+  void RemoveHandler(int id) {
+    auto result = std::find_if(handler_list_.cbegin(), handler_list_.cend(),
+                               [id](const std::pair<int, std::function<T>>& d) {
+                                 return d.first == id;
+                               });
+    if (result != handler_list_.cend()) {
+      handler_list_.erase(result);
+    }
+  }
+
+  HandlerRegistryIterator<T> begin() const {
+    return HandlerRegistryIterator<T>(handler_list_.begin());
+  }
+
+  HandlerRegistryIterator<T> end() const {
+    return HandlerRegistryIterator<T>(handler_list_.begin());
+  }
+
+ private:
+  int current_id_ = 1;
+  std::vector<std::pair<int, std::function<T>>> handler_list_;
+};
+}  // namespace cru
diff --git a/include/cru/common/Logger.hpp b/include/cru/common/Logger.hpp
index 4ea17c09..daf2e7d2 100644
--- a/include/cru/common/Logger.hpp
+++ b/include/cru/common/Logger.hpp
@@ -40,6 +40,7 @@ class Logger : public Object {
   std::list<std::unique_ptr<ILogSource>> sources_;
 };
 
+// TODO: Remove argument evaluation in Debug.
 template <typename... TArgs>
 void Debug([[maybe_unused]] TArgs&&... args) {
 #ifdef CRU_DEBUG
@@ -66,6 +67,7 @@ void Error(TArgs&&... args) {
                              fmt::format(std::forward<TArgs>(args)...));
 }
 
+// TODO: Remove argument evaluation in Debug.
 template <typename... TArgs>
 void TagDebug([[maybe_unused]] std::u16string_view tag,
               [[maybe_unused]] TArgs&&... args) {
diff --git a/include/cru/common/SelfResolvable.hpp b/include/cru/common/SelfResolvable.hpp
index 94f3ae87..eaa4ce34 100644
--- a/include/cru/common/SelfResolvable.hpp
+++ b/include/cru/common/SelfResolvable.hpp
@@ -39,9 +39,27 @@ class SelfResolvable {
   SelfResolvable() : resolver_(new T*(static_cast<T*>(this))) {}
   SelfResolvable(const SelfResolvable&) = delete;
   SelfResolvable& operator=(const SelfResolvable&) = delete;
-  SelfResolvable(SelfResolvable&&) = delete;
-  SelfResolvable& operator=(SelfResolvable&&) = delete;
-  virtual ~SelfResolvable() { (*resolver_) = nullptr; }
+
+  // Resolvers to old object will resolve to new object.
+  SelfResolvable(SelfResolvable&& other)
+      : resolver_(std::move(other.resolver_)) {
+    (*resolver_) = static_cast<T*>(this);
+  }
+
+  // Old resolvers for this object will resolve to nullptr.
+  // Other's resolvers will now resolve to this.
+  SelfResolvable& operator=(SelfResolvable&& other) {
+    if (this != &other) {
+      (*resolver_) = nullptr;
+      resolver_ = std::move(other.resolver_);
+      (*resolver_) = static_cast<T*>(this);
+    }
+    return *this;
+  }
+
+  virtual ~SelfResolvable() {
+    if (resolver_ != nullptr) (*resolver_) = nullptr;
+  }
 
   ObjectResolver<T> CreateResolver() { return ObjectResolver<T>(resolver_); }
 
diff --git a/include/cru/common/StringUtil.hpp b/include/cru/common/StringUtil.hpp
index 5dacfa12..62999d53 100644
--- a/include/cru/common/StringUtil.hpp
+++ b/include/cru/common/StringUtil.hpp
@@ -1,6 +1,10 @@
 #pragma once
 #include "Base.hpp"
 
+#include <functional>
+#include <string>
+#include <string_view>
+
 namespace cru {
 using CodePoint = std::int32_t;
 constexpr CodePoint k_invalid_code_point = -1;
@@ -124,4 +128,21 @@ void Utf16EncodeCodePointAppend(CodePoint code_point, std::u16string& str);
 
 std::string ToUtf8(std::u16string_view s);
 std::u16string ToUtf16(std::string_view s);
+
+// If given s is not a valid utf16 string, return value is UD.
+bool Utf16IsValidInsertPosition(std::u16string_view s, gsl::index position);
+
+// Return position after the character making predicate returns true or 0 if no
+// character doing so.
+gsl::index Utf16BackwardUntil(std::u16string_view str, gsl::index position,
+                              const std::function<bool(CodePoint)>& predicate);
+// Return position before the character making predicate returns true or
+// str.size() if no character doing so.
+gsl::index Utf16ForwardUntil(std::u16string_view str, gsl::index position,
+                             const std::function<bool(CodePoint)>& predicate);
+
+gsl::index Utf16PreviousWord(std::u16string_view str, gsl::index position,
+                             bool* is_space = nullptr);
+gsl::index Utf16NextWord(std::u16string_view str, gsl::index position,
+                         bool* is_space = nullptr);
 }  // namespace cru