Prefer std::string over std::wstring. (#179)

In the past, FTXUI switched from std::string to std::wstring to support
fullwidth characters. The reasons was that fullwidth characters can be
stored inside a single wchar_t.

Then FTXUI added support for combining characters. A single glygh
doesn't even fit a wchar_t. Instead, a glyph can be arbitrary large.

The usage of wstring doesn't really fit the new model and have several
drawbacks:
1. It doesn't simplify the implementation of FTXUI, because of combining
   characters.
2. It reduces drawing performance by 2x.
3. It increase Screen's memory allocation by 2x.

This patch converts FTXUI to use std::string internally. It now exposes
std::string based API. The std::wstring API remains, but is now
deprecated.

Tests and examples haven't been update to show the breakage is limited.
They will be updated in a second set of patches.

Bug: https://github.com/ArthurSonzogni/FTXUI/issues/153
Co-authored-by: Tushar Maheshwari <tushar27192@gmail.com>

include/ftxui/component/component.hpp

@@ -9,7 +9,7 @@
 #include "ftxui/component/component_base.hpp"     // for Component, Components
 #include "ftxui/component/component_options.hpp"  // for ButtonOption, CheckboxOption, InputOption, MenuOption, RadioboxOption, ToggleOption
 #include "ftxui/dom/elements.hpp"                 // for Element
-#include "ftxui/util/ref.hpp"  // for Ref, ConstStringRef, StringRef
+#include "ftxui/util/ref.hpp"  // for Ref, ConstStringRef, ConstStringListRef, StringRef
 
 namespace ftxui {
 struct ButtonOption;
@@ -34,17 +34,17 @@ Component Checkbox(ConstStringRef label,
 Component Input(StringRef content,
                 ConstStringRef placeholder,
                 Ref<InputOption> option = {});
-Component Menu(const std::vector<std::wstring>* entries,
+Component Menu(ConstStringListRef entries,
                int* selected_,
                Ref<MenuOption> = {});
-Component Radiobox(const std::vector<std::wstring>* entries,
+Component Radiobox(ConstStringListRef entries,
                    int* selected_,
                    Ref<RadioboxOption> option = {});
-Component Toggle(const std::vector<std::wstring>* entries,
+Component Toggle(ConstStringListRef entries,
                  int* selected,
                  Ref<ToggleOption> option = {});
 template <class T>  // T = {int, float, long}
-Component Slider(StringRef label, T* value, T min, T max, T increment);
+Component Slider(ConstStringRef label, T* value, T min, T max, T increment);
 Component ResizableSplitLeft(Component main, Component back, int* main_size);
 Component ResizableSplitRight(Component main, Component back, int* main_size);
 Component ResizableSplitTop(Component main, Component back, int* main_size);
@@ -65,6 +65,9 @@ Component Tab(Components children, int* selector);
 
 }  // namespace ftxui
 
+// Include component using the old deprecated wstring.
+#include "ftxui/component/deprecated.hpp"
+
 #endif /* end of include guard: FTXUI_COMPONENT_HPP */
 
 // Copyright 2021 Arthur Sonzogni. All rights reserved.

include/ftxui/component/component_options.hpp

@@ -33,10 +33,10 @@ struct ButtonOption {
 /// @brief Option for the Checkbox component.
 /// @ingroup component
 struct CheckboxOption {
-  std::wstring style_checked = L"▣ ";    ///< Prefix for a "checked" state.
-  std::wstring style_unchecked = L"☐ ";  ///< Prefix for a "unchecked" state.
-  Decorator style_focused = inverted;    ///< Decorator used when focused.
-  Decorator style_unfocused = nothing;   ///< Decorator used when unfocused.
+  std::string style_checked = "▣ ";     ///< Prefix for a "checked" state.
+  std::string style_unchecked = "☐ ";   ///< Prefix for a "unchecked" state.
+  Decorator style_focused = inverted;   ///< Decorator used when focused.
+  Decorator style_unfocused = nothing;  ///< Decorator used when unfocused.
 
   /// Called when the user change the state.
   std::function<void()> on_change = []() {};
@@ -59,10 +59,10 @@ struct InputOption {
 /// @brief Option for the Radiobox component.
 /// @ingroup component
 struct RadioboxOption {
-  std::wstring style_checked = L"◉ ";    ///< Prefix for a "checked" state.
-  std::wstring style_unchecked = L"○ ";  ///< Prefix for a "unchecked" state.
-  Decorator style_focused = inverted;    ///< Decorator used when focused.
-  Decorator style_unfocused = nothing;   ///< Decorator used when unfocused.
+  std::string style_checked = "◉ ";     ///< Prefix for a "checked" state.
+  std::string style_unchecked = "○ ";   ///< Prefix for a "unchecked" state.
+  Decorator style_focused = inverted;   ///< Decorator used when focused.
+  Decorator style_unfocused = nothing;  ///< Decorator used when unfocused.
 
   /// Called when the selected entry changes.
   std::function<void()> on_change = []() {};

include/ftxui/component/deprecated.hpp

@@ -0,0 +1,17 @@
+#ifndef FTXUI_COMPONENT_DEPRECATED_HPP
+#define FTXUI_COMPONENT_DEPRECATED_HPP
+
+#include "ftxui/component/component.hpp"
+
+namespace ftxui {
+
+Component Input(WideStringRef content,
+                ConstStringRef placeholder,
+                Ref<InputOption> option = {});
+}  // namespace ftxui
+
+#endif /* FTXUI_COMPONENT_DEPRECATED_HPP */
+
+// Copyright 2021 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.

include/ftxui/component/event.hpp

@@ -24,10 +24,9 @@ class ComponentBase;
 /// https://invisible-island.net/xterm/ctlseqs/ctlseqs.html
 struct Event {
   // --- Constructor section ---------------------------------------------------
+  static Event Character(std::string);
   static Event Character(char);
   static Event Character(wchar_t);
-
-  static Event Character(std::string);
   static Event Special(std::string);
   static Event Mouse(std::string, Mouse mouse);
   static Event CursorReporting(std::string, int x, int y);
@@ -58,7 +57,7 @@ struct Event {
 
   //--- Method section ---------------------------------------------------------
   bool is_character() const { return type_ == Type::Character; }
-  wchar_t character() const { return character_; }
+  std::string character() const { return input_; }
 
   bool is_mouse() const { return type_ == Type::Mouse; }
   struct Mouse& mouse() {
@@ -92,7 +91,6 @@ struct Event {
   };
 
   union {
-    wchar_t character_ = U'?';
     struct Mouse mouse_;
     struct Cursor cursor_;
   };