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Chapter17/cib/libs/flow/detail/walk.hpp

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+#pragma once
+
+#include <flow/subgraph_identity.hpp>
+
+#include <stdx/concepts.hpp>
+#include <stdx/tuple.hpp>
+#include <stdx/type_traits.hpp>
+
+#include <utility>
+
+namespace flow::dsl {
+template <typename T>
+concept subgraph = requires { typename stdx::remove_cvref_t<T>::is_subgraph; };
+
+template <typename Source, typename Dest, typename Cond> struct edge {
+    using source_t = Source;
+    using dest_t = Dest;
+    using cond_t = Cond;
+};
+
+constexpr inline class get_initials_t {
+    template <subgraph N>
+    friend constexpr auto tag_invoke(get_initials_t, N &&n) {
+        return stdx::make_tuple(std::forward<N>(n));
+    }
+
+  public:
+    template <typename... Ts>
+    constexpr auto operator()(Ts &&...ts) const
+        noexcept(noexcept(tag_invoke(std::declval<get_initials_t>(),
+                                     std::forward<Ts>(ts)...)))
+            -> decltype(tag_invoke(*this, std::forward<Ts>(ts)...)) {
+        return tag_invoke(*this, std::forward<Ts>(ts)...);
+    }
+} get_initials{};
+
+constexpr inline class get_finals_t {
+    template <subgraph N>
+    friend constexpr auto tag_invoke(get_finals_t, N &&n) {
+        return stdx::make_tuple(std::forward<N>(n));
+    }
+
+  public:
+    template <typename... Ts>
+    constexpr auto operator()(Ts &&...ts) const
+        noexcept(noexcept(tag_invoke(std::declval<get_finals_t>(),
+                                     std::forward<Ts>(ts)...)))
+            -> decltype(tag_invoke(*this, std::forward<Ts>(ts)...)) {
+        return tag_invoke(*this, std::forward<Ts>(ts)...);
+    }
+} get_finals{};
+
+constexpr inline class get_nodes_t {
+    template <subgraph N> friend constexpr auto tag_invoke(get_nodes_t, N &&n) {
+        if constexpr (std::remove_cvref_t<N>::identity ==
+                      subgraph_identity::REFERENCE) {
+            return stdx::tuple{};
+        } else {
+            return stdx::make_tuple(std::forward<N>(n));
+        }
+    }
+
+  public:
+    template <typename... Ts>
+    constexpr auto operator()(Ts &&...ts) const
+        noexcept(noexcept(tag_invoke(std::declval<get_nodes_t>(),
+                                     std::forward<Ts>(ts)...)))
+            -> decltype(tag_invoke(*this, std::forward<Ts>(ts)...)) {
+        return tag_invoke(*this, std::forward<Ts>(ts)...);
+    }
+} get_nodes{};
+
+constexpr inline class get_all_mentioned_nodes_t {
+    template <subgraph N>
+    friend constexpr auto tag_invoke(get_all_mentioned_nodes_t, N &&n) {
+        return stdx::make_tuple(std::forward<N>(n));
+    }
+
+  public:
+    template <typename... Ts>
+    constexpr auto operator()(Ts &&...ts) const
+        noexcept(noexcept(tag_invoke(std::declval<get_all_mentioned_nodes_t>(),
+                                     std::forward<Ts>(ts)...)))
+            -> decltype(tag_invoke(*this, std::forward<Ts>(ts)...)) {
+        return tag_invoke(*this, std::forward<Ts>(ts)...);
+    }
+} get_all_mentioned_nodes{};
+
+constexpr inline class get_edges_t {
+    friend constexpr auto tag_invoke(get_edges_t, subgraph auto const &) {
+        return stdx::tuple{};
+    }
+
+  public:
+    template <typename... Ts>
+    constexpr auto operator()(Ts &&...ts) const
+        noexcept(noexcept(tag_invoke(std::declval<get_edges_t>(),
+                                     std::forward<Ts>(ts)...)))
+            -> decltype(tag_invoke(*this, std::forward<Ts>(ts)...)) {
+        return tag_invoke(*this, std::forward<Ts>(ts)...);
+    }
+} get_edges{};
+} // namespace flow::dsl