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diff --git a/tiger-compiler/lib/misc/xalloc.hh b/tiger-compiler/lib/misc/xalloc.hh
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+++ b/tiger-compiler/lib/misc/xalloc.hh
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+/**
+ ** \file misc/xalloc.hh
+ ** \brief Declaration of misc::xalloc.
+ **/
+
+#pragma once
+
+#include <functional>
+#include <iostream>
+
+namespace misc
+{
+  /// Defines the operator() for the classes get_type, set_type and swap_type.
+  struct iomanipulator
+  {
+    virtual ~iomanipulator() = default;
+    virtual void operator()(std::ostream& o) const = 0;
+  };
+
+  /** \brief Launch the iomanipulator action on o.
+   **
+   ** Call the operator() of g (so set, get or swap the
+   ** xalloced data with data_).
+   */
+  std::ostream& operator<<(std::ostream& o, const iomanipulator& g);
+
+  /** \brief Allocate slots in std::ostreams.
+   **
+   ** Used to store flags in streams so that calling print
+   ** with additional parameters is no longer required (for
+   ** example in ast/libast.hh).
+   **
+   ** Set, get or swap data.
+   ** The idea is to build the right inner class with set, get or
+   ** swap methods, then use this class as a parameter of operator<<.
+   **
+   ** `StoredType` must be `CopyConstructible`. If it's not
+   ** `DefaultConstructible`, then arguments for its constructor are
+   ** to be passed to the `xalloc` constructor.
+   */
+  template <class StoredType> class xalloc
+  {
+  private:
+    /** \brief Handle the data to put in the xalloced place.
+     **
+     ** This inner class is used only with the set method.
+     */
+    class set_type : public iomanipulator
+    {
+    public:
+      /// Set data_ to data.
+      set_type(const xalloc& slot, StoredType& data);
+      /// Set the data in the xalloced place.
+      void operator()(std::ostream& ostr) const override;
+
+    private:
+      /// The xalloced data.
+      const xalloc& slot_;
+      /// Data to put in the stream.
+      StoredType& data_;
+    };
+
+    /** \brief Handle the data to get from the xalloced place.
+     **
+     ** This inner class is used only with the get method.
+     */
+    class get_type : public iomanipulator
+    {
+    public:
+      /// Set data_ to data.
+      get_type(const xalloc& slot, StoredType& data);
+
+      /// Get the data from the xalloced place.
+      void operator()(std::ostream& ostr) const override;
+
+    private:
+      /// The xalloced data.
+      const xalloc& slot_;
+      /// Variable in which we return the xalloc data.
+      StoredType& data_;
+    };
+
+    /** \brief Swap the data stored in the stream for a given one.
+     **
+     ** This inner class is used only with the swap method.
+     */
+    class swap_type : public iomanipulator
+    {
+    public:
+      /// Set data_ to data.
+      swap_type(const xalloc& slot, StoredType& data);
+
+      /// Swap the data from the xalloced place for a given one.
+      void operator()(std::ostream& ostr) const override;
+
+    private:
+      /// The xalloced data.
+      const xalloc& slot_;
+      /// Variable in which we store the data to be swapped.
+      StoredType& data_;
+    };
+
+    /// The index of the slot.
+    const long int index_;
+    // The model that is used to create new instances.
+    const StoredType model_;
+
+  public:
+    /// Allocates the slot.
+    template <typename... Args> xalloc(Args&&... args);
+
+    static void
+    deallocate(std::ios_base::event type, std::ios_base& ios, int index);
+
+    /// The xalloc index.
+    long int index() const;
+    /// The stored data as an lvalue.
+    StoredType& operator()(std::ostream& ostr) const;
+
+    /// A setter.
+    /// \param data where to find the value when the setter is executed.
+    set_type set(StoredType& data) const;
+
+    /// A getter.
+    /// \param data where to store the value when the getter is executed.
+    get_type get(StoredType& data) const;
+
+    /// A swapper.
+    /// \param data value to exchange when the swapper is executed.
+    swap_type swap(StoredType& data) const;
+  };
+
+} // namespace misc
+
+#include <misc/xalloc.hxx>