Rework context interface.

examples/asm-dom/demos/context.cpp

@@ -19,7 +19,8 @@ typedef extend_context_type_t<dom::context, username_tag> app_context;
 void
 internal_app_ui(app_context ctx)
 {
-    dom::text(ctx, alia::printf(ctx, "Welcome, %s!", ctx.get<username_tag>()));
+    dom::text(ctx,
+        alia::printf(ctx, "Welcome, %s!", get_object<username_tag>(ctx)));
 }
 
 // Our top-level UI function takes the context that the asm-dom wrapper provides
@@ -32,7 +33,7 @@ main_app_ui(dom::context ctx)
     readable<std::string> username = value("tmadden");
 
     // Extend the app context to include the username.
-    app_context app_ctx = ctx.add<username_tag>(username);
+    app_context app_ctx = add_object<username_tag>(ctx, username);
 
     // Pass that context along to the internal portions of the app UI...
     internal_app_ui(app_ctx);
@@ -54,52 +55,3 @@ init_demo(std::string dom_id)
 static demo the_demo("custom-context", init_demo);
 
 } // namespace custom_context
-
-namespace doubly_extended_context {
-
-// clang-format off
-/// [doubly-extended-context]
-ALIA_DEFINE_TAGGED_TYPE(username_tag, readable<std::string>&)
-ALIA_DEFINE_TAGGED_TYPE(api_key_tag, readable<std::string>&)
-
-typedef extend_context_type_t<dom::context, username_tag, api_key_tag>
-    app_context;
-
-void
-internal_app_ui(app_context ctx)
-{
-    dom::text(ctx, alia::printf(ctx, "Welcome, %s!", ctx.get<username_tag>()));
-    dom::text(ctx,
-        alia::printf(ctx,
-            "Your secret key is %s! Keep it safe!",
-            ctx.get<api_key_tag>()));
-}
-
-void
-main_app_ui(dom::context ctx)
-{
-    readable<std::string> username = value("tmadden");
-    readable<std::string> api_key = value("abc123");
-
-    app_context app_ctx =
-        ctx.add<username_tag>(username).add<api_key_tag>(api_key);
-
-    internal_app_ui(app_ctx);
-}
-/// [doubly-extended-context]
-// clang-format on
-
-void
-init_demo(std::string dom_id)
-{
-    static alia::system the_system;
-    static dom::system the_dom;
-
-    initialize(the_dom, the_system, dom_id, [](dom::context ctx) {
-        main_app_ui(ctx);
-    });
-}
-
-static demo the_demo("doubly-extended-context", init_demo);
-
-} // namespace doubly_extended_context

examples/asm-dom/dom.cpp

@@ -29,7 +29,7 @@ install_element_callback(
     char const* event_type)
 {
     auto external_id = externalize(&data.identity);
-    auto* system = &get<system_tag>(ctx);
+    auto* system = &get_object<system_tag>(ctx);
     data.callback = [=](emscripten::val v) {
         dom_event event(v);
         dispatch_targeted_event(*system, event, external_id);
@@ -73,7 +73,7 @@ text_node_(dom::context ctx, readable<string> text)
         data->node.object.create_as_text_node("");
     if (is_refresh_event(ctx))
     {
-        refresh_tree_node(get<tree_traversal_tag>(ctx), data->node);
+        refresh_tree_node(get_object<tree_traversal_tag>(ctx), data->node);
         refresh_signal_shadow(
             data->value_id,
             text,
@@ -369,7 +369,7 @@ void
 system::operator()(alia::context vanilla_ctx)
 {
     tree_traversal<element_object> traversal;
-    auto ctx = vanilla_ctx.add<tree_traversal_tag>(traversal);
+    auto ctx = add_object<tree_traversal_tag>(vanilla_ctx, traversal);
 
     if (is_refresh_event(ctx))
     {

examples/asm-dom/dom.hpp

@@ -153,7 +153,7 @@ struct element_handle : noncopyable
         if (initializing_)
             node_->object.create_as_element(type);
         if (is_refresh_event(ctx))
-            refresh_tree_node(get<tree_traversal_tag>(ctx), *node_);
+            refresh_tree_node(get_object<tree_traversal_tag>(ctx), *node_);
     }
 
     template<class Value>
@@ -238,7 +238,7 @@ struct scoped_element : noncopyable
         if (initializing_)
             node_->object.create_as_element(type);
         if (is_refresh_event(ctx))
-            tree_scoping_.begin(get<tree_traversal_tag>(ctx), *node_);
+            tree_scoping_.begin(get_object<tree_traversal_tag>(ctx), *node_);
         return *this;
     }
 
@@ -386,7 +386,7 @@ cached_content(Context ctx, id_interface const& id, Function&& fn)
     if (is_refresh_event(ctx))
     {
         cacher.begin(
-            get<tree_traversal_tag>(ctx),
+            get_object<tree_traversal_tag>(ctx),
             data->caching,
             id,
             container.is_dirty());

examples/qt/adaptor.cpp

@@ -64,7 +64,7 @@ set_next_node(qt_traversal& traversal, qt_layout_node* node)
 void
 add_layout_node(dataless_qt_context ctx, qt_layout_node* node)
 {
-    qt_traversal& traversal = ctx.get<qt_traversal_tag>();
+    qt_traversal& traversal = get_object<qt_traversal_tag>(ctx);
     set_next_node(traversal, node);
     traversal.next_ptr = &node->next;
 }
@@ -89,7 +89,7 @@ void
 scoped_layout_container::begin(qt_context ctx, qt_layout_container* container)
 {
     on_refresh(ctx, [&](auto ctx) {
-        traversal_ = &ctx.get<qt_traversal_tag>();
+        traversal_ = &get_object<qt_traversal_tag>(ctx);
         qt_traversal& traversal = *traversal_;
 
         set_next_node(traversal, container);
@@ -141,11 +141,11 @@ do_label(qt_context ctx, readable<string> text)
     auto& label = get_cached_data<qt_label>(ctx);
 
     on_refresh(ctx, [&](auto ctx) {
-        auto& system = ctx.get<system_tag>();
+        auto& system = get_object<system_tag>(ctx);
 
         if (!label.object)
         {
-            auto& traversal = get<qt_traversal_tag>(ctx);
+            auto& traversal = get_object<qt_traversal_tag>(ctx);
             auto* parent = traversal.active_parent;
             label.object = new QLabel(parent);
             if (parent->isVisible())
@@ -194,13 +194,13 @@ do_button(qt_context ctx, readable<string> text, action<> on_click)
     auto& button = get_cached_data<qt_button>(ctx);
 
     on_refresh(ctx, [&](auto ctx) {
-        auto& system = get<system_tag>(ctx);
+        auto& system = get_object<system_tag>(ctx);
 
         refresh_component_identity(ctx, button.identity);
 
         if (!button.object)
         {
-            auto& traversal = get<qt_traversal_tag>(ctx);
+            auto& traversal = get_object<qt_traversal_tag>(ctx);
             auto* parent = traversal.active_parent;
             button.object = new QPushButton(parent);
             if (parent->isVisible())
@@ -268,13 +268,13 @@ do_text_control(qt_context ctx, duplex<string> text)
     auto& widget = get_cached_data<qt_text_control>(ctx);
 
     on_refresh(ctx, [&](auto ctx) {
-        auto& system = get<system_tag>(ctx);
+        auto& system = get_object<system_tag>(ctx);
 
         refresh_component_identity(ctx, widget.identity);
 
         if (!widget.object)
         {
-            auto& traversal = get<qt_traversal_tag>(ctx);
+            auto& traversal = get_object<qt_traversal_tag>(ctx);
             auto* parent = traversal.active_parent;
             widget.object = new QTextEdit(parent);
             if (parent->isVisible())
@@ -362,7 +362,7 @@ void
 qt_system::operator()(alia::context vanilla_ctx)
 {
     qt_traversal traversal;
-    qt_context ctx = vanilla_ctx.add<qt_traversal_tag>(traversal);
+    qt_context ctx = add_object<qt_traversal_tag>(vanilla_ctx, traversal);
 
     on_refresh(ctx, [&](auto ctx) {
         traversal.next_ptr = &this->root;

src/alia/context/interface.cpp

@@ -15,11 +15,16 @@ make_context(
     timing_subsystem& timing)
 {
     storage->content_id = &unit_id;
-    return make_context(detail::make_empty_structural_collection(storage))
-        .add<system_tag>(sys)
-        .add<event_traversal_tag>(event)
-        .add<timing_tag>(timing)
-        .add<data_traversal_tag>(data);
+    return add_object<data_traversal_tag>(
+        add_object<timing_tag>(
+            add_object<event_traversal_tag>(
+                add_object<system_tag>(
+                    make_context(
+                        detail::make_empty_structural_collection(storage)),
+                    sys),
+                event),
+            timing),
+        data);
 }
 
 struct scoped_context_content_id_data

src/alia/context/interface.hpp

@@ -45,6 +45,15 @@ ALIA_ADD_DIRECT_TAGGED_DATA_ACCESS(context_storage, event_traversal_tag, event)
 ALIA_ADD_DIRECT_TAGGED_DATA_ACCESS(context_storage, data_traversal_tag, data)
 ALIA_ADD_DIRECT_TAGGED_DATA_ACCESS(context_storage, timing_tag, timing)
 
+// Context objects implement this interface if they provide state that might
+// influence the component-level application code.
+struct stateful_context_object
+{
+    virtual id_interface const&
+    value_id()
+        = 0;
+};
+
 // the context interface wrapper
 template<class Contents>
 struct context_interface
@@ -78,41 +87,41 @@ struct context_interface
 
     typedef Contents contents_type;
 
-    template<class Tag>
-    bool
-    has() const
-    {
-        return detail::has_tagged_data<Tag>(contents_);
-    }
+    Contents contents_;
+};
 
-    template<class Tag, class Data>
-    auto
-    add(Data& data)
-    {
-        auto new_contents
-            = detail::add_tagged_data<Tag>(contents_, std::ref(data));
-        return context_interface<decltype(new_contents)>(
-            std::move(new_contents));
-    }
+// manipulation of context objects...
 
-    template<class Tag>
-    auto
-    remove()
-    {
-        auto new_contents = detail::remove_tagged_data<Tag>(contents_);
-        return context_interface<decltype(new_contents)>(
-            std::move(new_contents));
-    }
+template<class Tag, class Contents>
+bool
+has_object(context_interface<Contents> ctx)
+{
+    return detail::has_tagged_data<Tag>(ctx.contents_);
+}
 
-    template<class Tag>
-    decltype(auto)
-    get()
-    {
-        return detail::get_tagged_data<Tag>(contents_);
-    }
+template<class Tag, class Contents, class Data>
+auto
+add_object(context_interface<Contents> ctx, Data& data)
+{
+    auto new_contents
+        = detail::add_tagged_data<Tag>(ctx.contents_, std::ref(data));
+    return context_interface<decltype(new_contents)>(std::move(new_contents));
+}
 
-    Contents contents_;
-};
+template<class Tag, class Contents>
+auto
+remove_object(context_interface<Contents> ctx)
+{
+    auto new_contents = detail::remove_tagged_data<Tag>(ctx.contents_);
+    return context_interface<decltype(new_contents)>(std::move(new_contents));
+}
+
+template<class Tag, class Contents>
+decltype(auto)
+get_object(context_interface<Contents> ctx)
+{
+    return detail::get_tagged_data<Tag>(ctx.contents_);
+}
 
 template<class Context, class... Tag>
 struct extend_context_type
@@ -180,25 +189,18 @@ copy_context(Context ctx)
     return Context(typename Context::contents_type(new_storage));
 }
 
-template<class Tag, class Contents>
-decltype(auto)
-get(context_interface<Contents> context)
-{
-    return context.template get<Tag>();
-}
-
 template<class Context>
 event_traversal&
 get_event_traversal(Context ctx)
 {
-    return ctx.template get<event_traversal_tag>();
+    return get_object<event_traversal_tag>(ctx);
 }
 
 template<class Context>
 data_traversal&
 get_data_traversal(Context ctx)
 {
-    return ctx.template get<data_traversal_tag>();
+    return get_object<data_traversal_tag>(ctx);
 }
 
 inline id_interface const&

src/alia/flow/events.hpp

@@ -238,7 +238,7 @@ template<class Context>
 void
 isolate_errors(Context ctx, function_view<void()> const& function)
 {
-    isolate_errors(get<system_tag>(ctx), function);
+    isolate_errors(get_object<system_tag>(ctx), function);
 }
 
 void

src/alia/flow/try_catch.cpp

@@ -8,7 +8,7 @@ try_block::try_block(context ctx) : ctx_(ctx)
 {
     get_cached_data(ctx, &data_);
     on_refresh(ctx, [&](auto ctx) {
-        auto refresh_counter = get<system_tag>(ctx).refresh_counter;
+        auto refresh_counter = get_object<system_tag>(ctx).refresh_counter;
         if (data_->last_refresh != refresh_counter)
         {
             data_->exception = nullptr;

src/alia/signals/async.hpp

@@ -160,7 +160,7 @@ async(Context ctx, Launcher launcher, Args const&... args)
                 auto reporter = async_reporter<Result>{
                     data_ptr,
                     data.version,
-                    &get<system_tag>(ctx),
+                    &get_object<system_tag>(ctx),
                     get_active_component_container(ctx)};
                 launcher(ctx, reporter, read_signal(args)...);
                 data.status = async_status::LAUNCHED;

src/alia/timing/ticks.cpp

@@ -11,7 +11,7 @@ schedule_animation_refresh(dataless_context ctx)
 {
     // Invoke the virtual method on the external system interface.
     // And also set a flag to indicate that a refresh is needed.
-    system& sys = ctx.get<system_tag>();
+    system& sys = get_object<system_tag>(ctx);
     if (!sys.refresh_needed)
     {
         if (sys.external)
@@ -26,7 +26,7 @@ millisecond_count
 get_raw_animation_tick_count(dataless_context ctx)
 {
     schedule_animation_refresh(ctx);
-    return ctx.get<timing_tag>().tick_counter;
+    return get_object<timing_tag>(ctx).tick_counter;
 }
 
 value_signal<millisecond_count>
@@ -38,7 +38,8 @@ get_animation_tick_count(dataless_context ctx)
 millisecond_count
 get_raw_animation_ticks_left(dataless_context ctx, millisecond_count end_time)
 {
-    int ticks_remaining = int(end_time - ctx.get<timing_tag>().tick_counter);
+    int ticks_remaining
+        = int(end_time - get_object<timing_tag>(ctx).tick_counter);
     if (ticks_remaining > 0)
     {
         if (is_refresh_event(ctx))