Component decorators (#354)

Add decorator variants for decorator components

Add the "pipe" operator for components, similar to what was done for Elements.
We are able to put something like:
```
Button(...) | Maybe(&show_button)
```

Add decorators for:
- `Maybe`
- `CatchEvent`
- `Renderer`

Signed-off-by: Kefu Chai <tchaikov@gmail.com>
Co-authored-by: ArthurSonzogni <sonzogniarthur@gmail.com>

CHANGELOG.md

@@ -23,6 +23,7 @@ Element gaugeDirection(float ratio, GaugeDirection);
   with others nearby.
 - Fix the `Table` rendering function, to allow automerging characters.
 - Bugfix: The `vscroll_indicator` now computes its offset and size correctly.
+- Add the `operator|=(Element, Decorator)`
 
 ### Component
 - Support SIGTSTP. (ctrl+z).
@@ -33,6 +34,14 @@ Element gaugeDirection(float ratio, GaugeDirection);
 - **bugfix** Automatically convert '\r' keys into '\n' for Linux programs that
   do not send the correct code for the return key, like the 'bind'.
   https://github.com/ArthurSonzogni/FTXUI/issues/337
+- Add decorator for components:
+  - `operator|(Component, ComponentDecorator)`
+  - `operator|=(Component, ComponentDecorator)`
+  - `operator|(Component, ElementDecorator)`
+  - `operator|=(Component, ElementDecorator)`
+  - Add the `Maybe` decorator.
+  - Add the `CatchEvent` decorator.
+  - Add the `Renderer` decorator.
 
 2.0.0
 -----

CMakeLists.txt

@@ -112,6 +112,7 @@ add_library(component
   src/ftxui/component/terminal_input_parser.cpp
   src/ftxui/component/terminal_input_parser.hpp
   src/ftxui/component/toggle.cpp
+  src/ftxui/component/util.cpp
 )
 
 target_link_libraries(dom

examples/component/maybe.cpp

@@ -1,17 +1,15 @@
-#include <memory>  // for shared_ptr, __shared_ptr_access
+#include <memory>  // for allocator, shared_ptr
-#include <string>  // for string, basic_string, allocator
+#include <string>  // for string, basic_string
 #include <vector>  // for vector
 
 #include "ftxui/component/captured_mouse.hpp"  // for ftxui
-#include "ftxui/component/component.hpp"  // for Checkbox, Maybe, Radiobox, Renderer, Vertical
+#include "ftxui/component/component.hpp"  // for operator|, Maybe, Checkbox, Radiobox, Renderer, Vertical
-#include "ftxui/component/component_base.hpp"  // for ComponentBase
+#include "ftxui/component/component_base.hpp"      // for Component
-#include "ftxui/component/screen_interactive.hpp"  // for Component, ScreenInteractive
+#include "ftxui/component/screen_interactive.hpp"  // for ScreenInteractive
-#include "ftxui/dom/elements.hpp"  // for Element, operator|, border
+#include "ftxui/dom/elements.hpp"  // for border, color, operator|, text, Element
+#include "ftxui/screen/color.hpp"  // for Color, Color::Red
 
 using namespace ftxui;
-Component Border(Component child) {
-  return Renderer(child, [child] { return child->Render() | border; });
-}
 
 int main(int argc, const char* argv[]) {
   std::vector<std::string> entries = {
@@ -21,20 +19,19 @@ int main(int argc, const char* argv[]) {
   };
   int menu_1_selected = 0;
   int menu_2_selected = 0;
-  auto menu_1 = Radiobox(&entries, &menu_1_selected);
-  auto menu_2 = Radiobox(&entries, &menu_2_selected);
-
-  menu_1 = Border(menu_1);
-  menu_2 = Border(menu_2);
 
   bool menu_1_show = false;
   bool menu_2_show = false;
 
   auto layout = Container::Vertical({
       Checkbox("Show menu_1", &menu_1_show),
-      Maybe(menu_1, &menu_1_show),
+      Radiobox(&entries, &menu_1_selected) | border | Maybe(&menu_1_show),
       Checkbox("Show menu_2", &menu_2_show),
-      Maybe(menu_2, &menu_2_show),
+      Radiobox(&entries, &menu_2_selected) | border | Maybe(&menu_2_show),
+
+      Renderer([] {
+        return text("You found the secret combinaison!") | color(Color::Red);
+      }) | Maybe([&] { return menu_1_selected == 1 && menu_2_selected == 2; }),
   });
 
   auto screen = ScreenInteractive::TerminalOutput();

examples/component/print_key_press.cpp

@@ -84,7 +84,7 @@ int main(int argc, const char* argv[]) {
     return window(text("keys"), vbox(std::move(children)));
   });
 
-  component = CatchEvent(component, [&](Event event) {
+  component |= CatchEvent([&](Event event) {
     keys.push_back(event);
     return true;
   });

examples/dom/hflow.cpp

@@ -1,4 +1,3 @@
-#include <stddef.h>                // for size_t
 #include <stdio.h>                 // for getchar
 #include <ftxui/dom/elements.hpp>  // for operator|, size, Element, text, hcenter, Decorator, Fit, WIDTH, hflow, window, EQUAL, GREATER_THAN, HEIGHT, bold, border, dim, LESS_THAN
 #include <ftxui/screen/screen.hpp>  // for Full, Screen

examples/dom/vflow.cpp

@@ -1,4 +1,3 @@
-#include <stddef.h>                // for size_t
 #include <stdio.h>                 // for getchar
 #include <ftxui/dom/elements.hpp>  // for operator|, Element, size, text, hcenter, Fit, vflow, window, EQUAL, bold, border, dim, HEIGHT, WIDTH
 #include <ftxui/screen/screen.hpp>  // for Full, Screen

include/ftxui/component/component.hpp

@@ -4,6 +4,7 @@
 #include <functional>  // for function
 #include <memory>      // for make_shared, shared_ptr
 #include <string>      // for wstring
+#include <utility>     // for forward
 #include <vector>      // for vector
 
 #include "ftxui/component/component_base.hpp"     // for Component, Components
@@ -26,6 +27,14 @@ std::shared_ptr<T> Make(Args&&... args) {
   return std::make_shared<T>(std::forward<Args>(args)...);
 }
 
+// Pipe operator to decorate components.
+using ComponentDecorator = std::function<Component(Component)>;
+using ElementDecorator = std::function<Element(Element)>;
+Component operator|(Component component, ComponentDecorator decorator);
+Component operator|(Component component, ElementDecorator decorator);
+Component& operator|=(Component& component, ComponentDecorator decorator);
+Component& operator|=(Component& component, ElementDecorator decorator);
+
 namespace Container {
 Component Vertical(Components children);
 Component Vertical(Components children, int* selector);
@@ -38,38 +47,55 @@ Component Tab(Components children, int* selector);
 Component Button(ConstStringRef label,
                  std::function<void()> on_click,
                  Ref<ButtonOption> = {});
+
 Component Checkbox(ConstStringRef label,
                    bool* checked,
                    Ref<CheckboxOption> option = {});
+
 Component Input(StringRef content,
                 ConstStringRef placeholder,
                 Ref<InputOption> option = {});
+
 Component Menu(ConstStringListRef entries,
                int* selected_,
                Ref<MenuOption> = {});
+
 Component MenuEntry(ConstStringRef label, Ref<MenuEntryOption> = {});
+
 Component Dropdown(ConstStringListRef entries, int* selected);
+
 Component Radiobox(ConstStringListRef entries,
                    int* selected_,
                    Ref<RadioboxOption> option = {});
+
 Component Toggle(ConstStringListRef entries,
                  int* selected,
                  Ref<ToggleOption> option = {});
+
 template <class T>  // T = {int, float, long}
 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);
 Component ResizableSplitBottom(Component main, Component back, int* main_size);
+
 Component Renderer(Component child, std::function<Element()>);
 Component Renderer(std::function<Element()>);
 Component Renderer(std::function<Element(bool /* focused */)>);
+ComponentDecorator Renderer(ElementDecorator);
+
 Component CatchEvent(Component child, std::function<bool(Event)>);
+ComponentDecorator CatchEvent(std::function<bool(Event)> on_event);
+
 Component Maybe(Component, const bool* show);
+Component Maybe(Component, std::function<bool()>);
+ComponentDecorator Maybe(const bool* show);
+ComponentDecorator Maybe(std::function<bool()>);
+
 Component Collapsible(ConstStringRef label,
                       Component child,
                       Ref<bool> show = false);
-
 }  // namespace ftxui
 
 // Include component using the old deprecated wstring.

include/ftxui/component/deprecated.hpp

@@ -5,9 +5,10 @@
 
 namespace ftxui {
 
-Component Input(WideStringRef content,
+[[deprecated("use Input with normal std::string instead.")]] Component Input(
-                ConstStringRef placeholder,
+    WideStringRef content,
-                Ref<InputOption> option = {});
+    ConstStringRef placeholder,
+    Ref<InputOption> option = {});
 }  // namespace ftxui
 
 #endif /* FTXUI_COMPONENT_DEPRECATED_HPP */

include/ftxui/dom/elements.hpp

@@ -28,6 +28,7 @@ enum class GaugeDirection { Left, Up, Right, Down };
 // -> text("ftxui") | bold | underlined
 // -> underlined(bold(text("FTXUI")))
 Element operator|(Element, Decorator);
+Element& operator|=(Element&, Decorator);
 Elements operator|(Elements, Decorator);
 Decorator operator|(Decorator, Decorator);
 

src/ftxui/component/catch_event.cpp

@@ -55,6 +55,33 @@ Component CatchEvent(Component child,
   return out;
 }
 
+/// @brief Decorate a component, using |on_event| to catch events. This function
+/// must returns true when the event has been handled, false otherwise.
+/// @param on_event The function drawing the interface.
+/// @ingroup component
+///
+/// ### Example
+///
+/// ```cpp
+/// auto screen = ScreenInteractive::TerminalOutput();
+/// auto renderer = Renderer([] { return text("Hello world"); });
+/// renderer |= CatchEvent([&](Event event) {
+///   if (event == Event::Character('q')) {
+///     screen.ExitLoopClosure()();
+///     return true;
+///   }
+///   return false;
+/// });
+/// screen.Loop(renderer);
+/// ```
+ComponentDecorator CatchEvent(std::function<bool(Event)> on_event) {
+  return [on_event = std::move(on_event)](Component child) {
+    return CatchEvent(child, [on_event = std::move(on_event)](Event event) {
+      return on_event(event);
+    });
+  };
+}
+
 }  // namespace ftxui
 
 // Copyright 2021 Arthur Sonzogni. All rights reserved.

src/ftxui/component/maybe.cpp

@@ -1,38 +1,86 @@
+#include <functional>  // for function
 #include <memory>  // for make_unique, __shared_ptr_access, __shared_ptr_access<>::element_type, shared_ptr
 #include <utility>  // for move
 
-#include "ftxui/component/component.hpp"       // for Make, Maybe
+#include "ftxui/component/component.hpp"  // for ComponentDecorator, Maybe, Make
-#include "ftxui/component/component_base.hpp"  // for ComponentBase, Component
+#include "ftxui/component/component_base.hpp"  // for Component, ComponentBase
 #include "ftxui/component/event.hpp"           // for Event
 #include "ftxui/dom/elements.hpp"              // for Element
 #include "ftxui/dom/node.hpp"                  // for Node
 
 namespace ftxui {
 
-Component Maybe(Component child, const bool* show) {
+Component Maybe(Component child, std::function<bool()> show) {
   class Impl : public ComponentBase {
    public:
-    Impl(const bool* show) : show_(show) {}
+    Impl(std::function<bool()> show) : show_(std::move(show)) {}
 
    private:
     Element Render() override {
-      return *show_ ? ComponentBase::Render() : std::make_unique<Node>();
+      return show_() ? ComponentBase::Render() : std::make_unique<Node>();
     }
     bool Focusable() const override {
-      return *show_ && ComponentBase::Focusable();
+      return show_() && ComponentBase::Focusable();
     }
     bool OnEvent(Event event) override {
-      return *show_ && ComponentBase::OnEvent(event);
+      return show_() && ComponentBase::OnEvent(event);
     }
 
-    const bool* show_;
+    std::function<bool()> show_;
   };
 
-  auto maybe = Make<Impl>(show);
+  auto maybe = Make<Impl>(std::move(show));
   maybe->Add(std::move(child));
   return maybe;
 }
 
+/// @brief Decorate a component. It is shown only when the |show| function
+/// returns true.
+/// @params show a function returning whether the decoratorated component should
+/// be shown.
+/// @ingroup component
+///
+/// ### Example
+///
+/// ```cpp
+/// auto component = Renderer([]{ return "Hello World!"; });
+/// auto maybe_component = component | Maybe([&]{ return counter == 42; });
+/// ```
+ComponentDecorator Maybe(std::function<bool()> show) {
+  return [show = std::move(show)](Component child) mutable {
+    return Maybe(child, std::move(show));
+  };
+}
+
+/// @brief Decorate a component |child|. It is shown only when |show| is true.
+/// @params child the compoennt to decorate.
+/// @params show a boolean. |child| is shown when |show| is true.
+/// @ingroup component
+///
+/// ### Example
+///
+/// ```cpp
+/// auto component = Renderer([]{ return "Hello World!"; });
+/// auto maybe_component = Maybe(component, &show);
+/// ```
+Component Maybe(Component child, const bool* show) {
+  return Maybe(child, [show] { return *show; });
+}
+
+/// @brief Decorate a component. It is shown only when |show| is true.
+/// @params show a boolean. |child| is shown when |show| is true.
+/// @ingroup component
+///
+/// ### Example
+///
+/// ```cpp
+/// auto component = Renderer([]{ return "Hello World!"; });
+/// auto maybe_component = component | Maybe(&show);
+/// ```
+ComponentDecorator Maybe(const bool* show) {
+  return [show](Component child) { return Maybe(child, show); };
+}
+
 }  // namespace ftxui
 
 // Copyright 2021 Arthur Sonzogni. All rights reserved.

src/ftxui/component/renderer.cpp

@@ -104,6 +104,28 @@ Component Renderer(std::function<Element(bool)> render) {
   return Make<Impl>(std::move(render));
 }
 
+/// @brief Decorate a component, by decorating what it renders.
+/// @param decorator the function modifying the element it renders.
+/// @ingroup component
+///
+/// ### Example
+///
+/// ```cpp
+/// auto screen = ScreenInteractive::TerminalOutput();
+/// auto renderer =
+//     Renderer([] { return text("Hello");)
+///  | Renderer(bold)
+///  | Renderer(inverted);
+/// screen.Loop(renderer);
+/// ```
+ComponentDecorator Renderer(ElementDecorator decorator) {
+  return [decorator](Component component) {
+    return Renderer(component, [component, decorator] {
+      return component->Render() | decorator;
+    });
+  };
+}
+
 }  // namespace ftxui
 
 // Copyright 2021 Arthur Sonzogni. All rights reserved.

src/ftxui/component/util.cpp

@@ -0,0 +1,32 @@
+#include <functional>  // for function
+#include <memory>      // for __shared_ptr_access
+
+#include "ftxui/component/component.hpp"  // for ElementDecorator, Renderer, ComponentDecorator, operator|, operator|=
+#include "ftxui/component/component_base.hpp"  // for Component, ComponentBase
+#include "ftxui/dom/elements.hpp"              // for Element
+
+namespace ftxui {
+
+Component operator|(Component component, ComponentDecorator decorator) {
+  return decorator(component);
+}
+
+Component operator|(Component component, ElementDecorator decorator) {
+  return component | Renderer(decorator);
+}
+
+Component& operator|=(Component& component, ComponentDecorator decorator) {
+  component = component | decorator;
+  return component;
+}
+
+Component& operator|=(Component& component, ElementDecorator decorator) {
+  component = component | decorator;
+  return component;
+}
+
+}  // namespace ftxui
+
+// Copyright 2022 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.

src/ftxui/dom/util.cpp

@@ -66,6 +66,22 @@ Element operator|(Element element, Decorator decorator) {
   return decorator(std::move(element));
 }
 
+/// @brief Apply a decorator to an element.
+/// @return the decorated element.
+/// @ingroup dom
+///
+/// ### Example
+///
+/// Both of these are equivalent:
+/// ```cpp
+/// auto element = text("Hello");
+/// element |= bold;
+/// ```
+Element& operator|=(Element& e, Decorator d) {
+  e = e | d;
+  return e;
+}
+
 /// The minimal dimension that will fit the given element.
 /// @see Fixed
 /// @see Full