add Chapter18

Chapter18/cib/libs/flow/builder.hpp

@@ -0,0 +1,27 @@
+#pragma once
+
+#include <flow/common.hpp>
+#include <flow/graph_builder.hpp>
+#include <flow/impl.hpp>
+
+#include <stdx/compiler.hpp>
+#include <stdx/ct_string.hpp>
+#include <stdx/panic.hpp>
+
+namespace flow {
+template <stdx::ct_string Name = "">
+using builder = graph<Name, graph_builder<Name, impl>>;
+
+template <stdx::ct_string Name = ""> struct service {
+    using builder_t = builder<Name>;
+    using interface_t = FunctionPtr;
+
+    CONSTEVAL static auto uninitialized() -> interface_t {
+        return [] {
+            using namespace stdx::literals;
+            stdx::panic<"Attempting to run flow ("_cts + Name +
+                        ") before it is initialized"_cts>();
+        };
+    }
+};
+} // namespace flow