Add flexibilty to object value IDs.

docs/flow-tracking.md

@@ -163,7 +163,7 @@ underlying data associated with each item will change when the item moves.*
 Depending on what you're associating with your items, the effects of this can
 vary from slight inefficiencies to complete discontinuities in your interface.
 
-You can override the default association by defining a `get_alia_id` function
+You can override the default association by defining a `get_alia_item_id` function
 for your item's type. (It should be accessible from within the `alia` namespace,
 either via [argument-dependent
 lookup](https://en.cppreference.com/w/cpp/language/adl) or because it's defined

src/alia/context/interface.hpp

@@ -214,14 +214,37 @@ struct has_value_id<
 {
 };
 
+} // namespace detail
+
+template<class Object>
+std::enable_if_t<detail::has_value_id<Object>::value, id_interface const&>
+get_alia_value_id(Object const& object)
+{
+    return object.value_id();
+}
+
+namespace detail {
+
+template<class Object, class = void_t<>>
+struct has_alia_value_id : std::false_type
+{
+};
+template<class Object>
+struct has_alia_value_id<
+    Object,
+    void_t<decltype(static_cast<id_interface const&>(
+        get_alia_value_id(std::declval<Object>())))>> : std::true_type
+{
+};
+
 void
 fold_in_content_id(context ctx, id_interface const& id);
 
 template<class Object>
-std::enable_if_t<has_value_id<Object>::value>
+std::enable_if_t<has_alia_value_id<Object>::value>
 fold_in_object_id(context ctx, Object const& object)
 {
-    fold_in_content_id(ctx, object.value_id());
+    fold_in_content_id(ctx, get_alia_value_id(object));
 }
 
 template<class Object>

src/alia/flow/for_each.hpp

@@ -43,7 +43,7 @@ struct is_vector_like<
 
 template<class Item>
 auto
-get_alia_id(Item const&)
+get_alia_item_id(Item const&)
 {
     return null_id;
 }
@@ -243,7 +243,7 @@ for_each(Context ctx, ContainerSignal const& container_signal, Fn&& fn)
                 ctx,
                 nc,
                 [&](named_block& nb) {
-                    auto iteration_id = get_alia_id(container[index]);
+                    auto iteration_id = get_alia_item_id(container[index]);
                     if (iteration_id != null_id)
                         nb.begin(nc, iteration_id);
                     else
@@ -283,9 +283,9 @@ for_each(Context ctx, Container&& container, Fn&& fn)
             ctx,
             nc,
             [&](named_block& nb) {
-                // We don't try to use get_alia_id() here because we want to
-                // support the use case where the UI is present even when the
-                // item isn't available, and we want to keep the block ID
+                // We don't try to use get_alia_item_id() here because we want
+                // to support the use case where the UI is present even when
+                // the item isn't available, and we want to keep the block ID
                 // stable in that scenario.
                 nb.begin(nc, make_id(index));
             },
@@ -322,7 +322,7 @@ for_each(Context ctx, Container&& container, Fn&& fn)
             ctx,
             nc,
             [&](named_block& nb) {
-                auto iteration_id = get_alia_id(item);
+                auto iteration_id = get_alia_item_id(item);
                 if (iteration_id != null_id)
                     nb.begin(nc, iteration_id);
                 else
@@ -416,7 +416,7 @@ for_each(Context ctx, ContainerSignal const& container_signal, Fn&& fn)
                 ctx,
                 nc,
                 [&](named_block& nb) {
-                    auto iteration_id = get_alia_id(item);
+                    auto iteration_id = get_alia_item_id(item);
                     if (iteration_id != null_id)
                         nb.begin(nc, iteration_id);
                     else
@@ -457,9 +457,9 @@ for_each(Context ctx, Container&& container, Fn&& fn)
             ctx,
             nc,
             [&](named_block& nb) {
-                // We don't try to use get_alia_id() here because we want to
-                // support the use case where the UI is present even when the
-                // item isn't available, and we want to keep the block ID
+                // We don't try to use get_alia_item_id() here because we want
+                // to support the use case where the UI is present even when
+                // the item isn't available, and we want to keep the block ID
                 // stable in that scenario.
                 nb.begin(nc, make_id(&item));
             },
@@ -496,7 +496,7 @@ for_each(Context ctx, Container&& container, Fn&& fn)
             ctx,
             nc,
             [&](named_block& nb) {
-                auto iteration_id = get_alia_id(item);
+                auto iteration_id = get_alia_item_id(item);
                 if (iteration_id != null_id)
                     nb.begin(nc, iteration_id);
                 else

unit_tests/flow/for_each.cpp

@@ -42,7 +42,7 @@ operator<(my_item a, my_item b)
 }
 
 auto
-get_alia_id(my_item const& item)
+get_alia_item_id(my_item const& item)
 {
     return make_id(item.id);
 }
@@ -327,7 +327,7 @@ TEST_CASE("item vector", "[flow][for_each]")
 
     std::reverse(container.begin(), container.end());
 
-    // Since my_item defines get_alia_id(), the graph data properly follows
+    // Since my_item defines get_alia_item_id(), the graph data properly follows
     // the items around, so there are no additional calls.
     check_traversal(sys, controller, "cherry;banana;apple;");
     REQUIRE(call_count == 3);
@@ -568,7 +568,7 @@ TEST_CASE("item list", "[for_each][list]")
 
     std::reverse(container.begin(), container.end());
 
-    // Since my_item defines get_alia_id(), the graph data properly follows
+    // Since my_item defines get_alia_item_id(), the graph data properly follows
     // the items around, so there are no additional calls.
     check_traversal(sys, controller, "cherry;banana;apple;");
     REQUIRE(call_count == 3);
@@ -654,7 +654,7 @@ TEST_CASE("for_each over a list of raw items", "[for_each][list]")
 
     std::reverse(container.begin(), container.end());
 
-    // Since my_item defines get_alia_id(), the graph data properly follows
+    // Since my_item defines get_alia_item_id(), the graph data properly follows
     // the items around, so there are no additional calls.
     check_traversal(sys, controller, "cherry;banana;apple;");
     REQUIRE(call_count == 3);