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diff --git a/tiger-compiler/lib/misc/unique.hh b/tiger-compiler/lib/misc/unique.hh
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+/**
+ ** \file misc/unique.hh
+ ** \brief Definition of misc::unique.
+ */
+
+#pragma once
+
+#include <iosfwd>
+#include <set>
+
+namespace misc
+{
+  /** \brief Define \c unique class.
+   **
+   ** Implementation of the flyweight pattern.
+   ** Map identical objects to a unique reference.
+   */
+  template <typename T, class C = std::less<T>> class unique
+  {
+  protected:
+    /// The unique's object type.
+    using object_set_type = std::set<T, C>;
+    /// The type for the size of the unique set.
+    using object_size_type = typename object_set_type::size_type;
+
+  public:
+    using value_type = unique;
+    using data_type = T;
+
+    /** \name Ctor & Dtor.
+     ** \{ */
+    /** \brief Construct a \c unique.
+     ** \param s referenced object */
+    unique(const data_type& s);
+    /** \brief Construct a \c unique.
+     ** \param u \c unique to copy. */
+    constexpr unique(const unique& u) = default;
+    virtual ~unique() = default;
+    /** \} */
+
+    /** \name Accessors.
+     ** \{ */
+    /// The object referenced by \c this.
+    const data_type& get() const;
+    operator const data_type&() const;
+
+    /// The number of referenced objects.
+    static object_size_type object_map_size();
+    /** \} */
+
+    /** \name Operators.
+     ** \{ */
+    /** \brief Assign a \c unique to this \c unique.
+     ** \param rhs \c unique to copy. */
+    value_type& operator=(const value_type& rhs);
+
+    /** \brief Compare two \c unique for equality.
+     ** \param rhs \c unique to compare with. */
+    bool operator==(const value_type& rhs) const;
+    /** \brief Compare two \c unique for inequality.
+     ** \param rhs \c unique to compare with. */
+    bool operator!=(const value_type& rhs) const;
+    /** \brief Compare two \c unique for order.
+     ** \param rhs \c unique to compare with. */
+    bool operator<(const value_type& rhs) const;
+    /** \} */
+
+  protected:
+    /// Return the set of uniques.
+    static object_set_type& object_set_instance();
+
+    /// Pointer to the unique referenced object.
+    const data_type* obj_;
+  };
+
+  /** \brief Intercept output stream redirection.
+   ** \param ostr the destination output stream
+   ** \param u a reference to the unique to redirect
+   */
+  template <typename T, class C>
+  std::ostream& operator<<(std::ostream& ostr, const unique<T, C>& u);
+
+} // namespace misc
+
+#include <misc/unique.hxx>