progress on session_insert_builder

include/matador/utils/uuid.hpp

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+#ifndef MATADOR_UUID_HPP
+#define MATADOR_UUID_HPP
+
+#include <array>
+#include <string>
+
+namespace matador::utils {
+
+class uuid {
+public:
+    using uuid_array = std::array<uint32_t, 4>;
+
+    // Default constructor initializes to zero
+    uuid() = default;
+
+    // Static UUID v4 generator
+    static uuid generate();
+
+    // Returns UUID as a string
+    [[nodiscard]] std::string str() const;
+
+    // Access to internal data
+    [[nodiscard]] const uuid_array& data() const;
+
+    // Reset UUID to zero
+    void clear() { _data.fill(0); }
+
+    // Comparisons
+    friend bool operator==(const uuid& lhs, const uuid& rhs);
+    friend bool operator!=(const uuid& lhs, const uuid& rhs);
+    friend bool operator<(const uuid& lhs, const uuid& rhs);
+
+private:
+    uuid_array _data{0, 0, 0, 0};
+};
+}
+
+// Hash specialization to allow use in unordered containers
+template <>
+struct std::hash<matador::utils::uuid> {
+    std::size_t operator()(const matador::utils::uuid& u) const noexcept {
+        std::size_t h = 0;
+        for (uint32_t val : u.data()) {
+            h ^= std::hash<uint32_t>{}(val) + 0x9e3779b9 + (h << 6) + (h >> 2);
+        }
+        return h;
+    }
+};
+
+#endif //MATADOR_UUID_HPP