Add {Const,}StringRef to simplify components.

include/ftxui/component/button.hpp

@@ -8,6 +8,7 @@
 #include "ftxui/component/component_base.hpp"  // for ComponentBase
 #include "ftxui/dom/elements.hpp"              // for Element
 #include "ftxui/screen/box.hpp"                // for Box
+#include "ftxui/screen/string.hpp"             // for ConstStringRef
 
 namespace ftxui {
 struct Event;
@@ -20,7 +21,7 @@ class ButtonBase : public ComponentBase {
   static ButtonBase* From(Component);
 
   // Constructor.
-  ButtonBase(const std::wstring* label, std::function<void()> on_click);
+  ButtonBase(ConstStringRef label, std::function<void()> on_click);
   ~ButtonBase() override = default;
 
   // Component implementation.
@@ -28,7 +29,7 @@ class ButtonBase : public ComponentBase {
   bool OnEvent(Event) override;
 
  private:
-  const std::wstring* label_;
+  ConstStringRef label_;
   std::function<void()> on_click_;
   Box box_;
 };

include/ftxui/component/checkbox.hpp

@@ -2,12 +2,13 @@
 #define FTXUI_COMPONENT_CHECKBOX_HPP
 
 #include <functional>  // for function
-#include <string>      // for wstring, allocator
+#include <string>      // for allocator, wstring
 
 #include "ftxui/component/component.hpp"       // for Component
 #include "ftxui/component/component_base.hpp"  // for ComponentBase
-#include "ftxui/dom/elements.hpp"  // for Element, Decorator, inverted, nothing
-#include "ftxui/screen/box.hpp"    // for Box
+#include "ftxui/dom/elements.hpp"   // for Element, Decorator, inverted, nothing
+#include "ftxui/screen/box.hpp"     // for Box
+#include "ftxui/screen/string.hpp"  // for ConstStringRef
 
 namespace ftxui {
 struct Event;
@@ -21,7 +22,7 @@ class CheckboxBase : public ComponentBase {
   static CheckboxBase* From(Component component);
 
   // Constructor.
-  CheckboxBase(const std::wstring* label, bool* state);
+  CheckboxBase(ConstStringRef label, bool* state);
   ~CheckboxBase() override = default;
 
 #if defined(_WIN32)
@@ -45,7 +46,7 @@ class CheckboxBase : public ComponentBase {
  private:
   bool OnMouseEvent(Event event);
 
-  const std::wstring* const label_;
+  ConstStringRef label_;
   bool* const state_;
   int cursor_position = 0;
   Box box_;

include/ftxui/component/component.hpp

@@ -7,6 +7,8 @@
 #include <vector>      // for vector
 
 #include "ftxui/component/component_base.hpp"
+#include "ftxui/dom/elements.hpp"   // for Element
+#include "ftxui/screen/string.hpp"  // for ConstStringRef, StringRef
 
 namespace ftxui {
 
@@ -20,9 +22,9 @@ std::shared_ptr<T> Make(Args&&... args) {
   return std::make_shared<T>(args...);
 }
 
-Component Button(const std::wstring* label, std::function<void()> on_click);
-Component Checkbox(const std::wstring* label, bool* checked);
-Component Input(std::wstring* content, const std::wstring* placeholder);
+Component Button(ConstStringRef label, std::function<void()> on_click);
+Component Checkbox(ConstStringRef label, bool* checked);
+Component Input(StringRef content, ConstStringRef placeholder);
 Component Menu(const std::vector<std::wstring>* entries, int* selected_);
 Component Radiobox(const std::vector<std::wstring>* entries, int* selected_);
 Component Toggle(const std::vector<std::wstring>* entries, int* selected);
@@ -30,7 +32,7 @@ Component Renderer(Component child, std::function<Element()>);
 Component Renderer(std::function<Element()>);
 
 template <class T>  // T = {int, float}
-Component Slider(std::wstring label, T* value, T min, T max, T increment);
+Component Slider(StringRef label, T* value, T min, T max, T increment);
 
 namespace Container {
 Component Vertical(Components children);

include/ftxui/component/input.hpp

@@ -8,6 +8,7 @@
 #include "ftxui/component/component_base.hpp"  // for ComponentBase
 #include "ftxui/dom/elements.hpp"              // for Element
 #include "ftxui/screen/box.hpp"                // for Box
+#include "ftxui/screen/string.hpp"             // for ConstStringRef, StringRef
 
 namespace ftxui {
 struct Event;
@@ -20,7 +21,7 @@ class InputBase : public ComponentBase {
   static InputBase* From(Component component);
 
   // Constructor.
-  InputBase(std::wstring* content, const std::wstring* placeholder);
+  InputBase(StringRef content, ConstStringRef placeholder);
   ~InputBase() override = default;
 
   // State.
@@ -35,8 +36,8 @@ class InputBase : public ComponentBase {
   bool OnEvent(Event) override;
 
  private:
-  std::wstring* const content_;
-  const std::wstring* const placeholder_;
+  StringRef content_;
+  ConstStringRef placeholder_;
 
   bool OnMouseEvent(Event);
   Box input_box_;

include/ftxui/screen/string.hpp

@@ -16,6 +16,41 @@ int wchar_width(wchar_t);
 int wchar_width_cjk(wchar_t);
 int wstring_width(const std::wstring&);
 int wstring_width_cjk(const std::wstring&);
+
+/// @brief For convenience, this class convert multiple mutable string
+/// references toward a shared representation.
+class StringRef {
+ public:
+  StringRef(std::wstring& ref);
+  StringRef(std::wstring* ref);
+  StringRef(const wchar_t* ref);
+  StringRef(const char* ref);
+
+  std::wstring& operator*();
+  std::wstring* operator->();
+
+ private:
+  std::wstring* const borrowed_ = nullptr;
+  std::wstring owned_;
+};
+
+/// @brief For convenience, this class convert multiple immutable string
+/// references toward  shared representation.
+class ConstStringRef {
+ public:
+  ConstStringRef(const std::wstring& ref);
+  ConstStringRef(const std::wstring* ref);
+  ConstStringRef(const wchar_t* ref);
+  ConstStringRef(const char* ref);
+
+  const std::wstring& operator*();
+  const std::wstring* operator->();
+
+ private:
+  const std::wstring* const borrowed_ = nullptr;
+  const std::wstring owned_;
+};
+
 }  // namespace ftxui
 
 #endif /* end of include guard: FTXUI_SCREEN_STRING_HPP */