First attempt

include/kpn/fixed_string.hpp

@@ -0,0 +1,46 @@
+#pragma once
+#include <algorithm>
+#include <string_view>
+#include <cstddef>
+
+namespace kpn {
+
+template<std::size_t N>
+struct fixed_string {
+    char data[N]{};
+
+    constexpr fixed_string(const char (&s)[N]) { std::copy_n(s, N, data); }
+    constexpr bool operator==(const fixed_string&) const = default;
+
+    template<std::size_t M>
+    constexpr bool operator==(const fixed_string<M>&) const { return false; }
+    constexpr std::string_view view() const { return {data, N - 1}; }
+};
+
+template<std::size_t N>
+fixed_string(const char (&)[N]) -> fixed_string<N>;
+
+// ── Port name pack lookup ─────────────────────────────────────────────────────
+
+inline constexpr std::size_t npos = std::size_t(-1);
+
+template<fixed_string Name, fixed_string... Names>
+constexpr std::size_t index_of() {
+    std::size_t i = 0;
+    bool found = false;
+    auto check = [&](auto n) {
+        if (!found) {
+            if (Name == n) found = true;
+            else           ++i;
+        }
+    };
+    (check(Names), ...);
+    return found ? i : npos;
+}
+
+// ── in<> / out<> name tag structs ─────────────────────────────────────────────
+
+template<fixed_string... Names> struct in  {};
+template<fixed_string... Names> struct out {};
+
+} // namespace kpn