glib/src/variant.hg

/* Copyright 2010 The glibmm Development Team
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library.  If not, see <http://www.gnu.org/licenses/>.
 */

_DEFS(glibmm,glib)

#include <glibmmconfig.h>
#include <glibmm/varianttype.h>
#include <glibmm/variantiter.h>
#include <glibmm/variantdbusstring.h>
#include <glibmm/refptr.h>
#include <glibmm/ustring.h>
#include <glibmm/error.h>
#include <utility>
#include <vector>
#include <map>
#include <memory>
#include <tuple>
#include <stdexcept>
#include <typeinfo>
#include <cstddef>

namespace Glib
{
class Bytes;

/** @defgroup Variant Variant Data Types
 *
 * The Variant classes deal with strongly typed
 * variant data. A Variant stores a value along with
 * information about the type of that value. The range of possible
 * values is determined by the type. The type system used is VariantType.
 *
 * See the VariantBase class and its derived types, such as VariantContainerBase,
 * and the Variant<> template type.
 *
 * Variant instances always have a type and a value (which are given
 * at construction time). The type and value of a Variant
 * can never change other than by the Variant itself being
 * destroyed.  A Variant cannot contain a pointer.
 *
 * Variant is heavily optimised for dealing with data in serialised
 * form. It works particularly well with data located in memory-mapped
 * files. It can perform nearly all deserialisation operations in a
 * small constant time, usually touching only a single memory page.
 * Serialised Variant data can also be sent over the network.
 *
 * Variant is largely compatible with D-Bus.  Almost all types of
 * Variant instances can be sent over D-Bus.  See VariantType for
 * exceptions.
 *
 * There is a Python-inspired text language for describing Variant
 * values. Variant includes a printer for this language and a parser
 * with type inferencing.
 */

//Note: We wrap this because it is thrown by GtkBuilder's functions.
// See https://bugzilla.gnome.org/show_bug.cgi?id=708206
// It would also be thrown by parse() if we wrap g_variant_parse().
// Now (2014-01-30) it's also thrown by Gio::Action::parse_detailed_name().
/** %Exception class for Variant parse errors.
 */
_WRAP_GERROR(VariantParseError, GVariantParseError, G_VARIANT_PARSE_ERROR, NO_GTYPE, decl_prefix GLIBMM_API)

//TODO: Add this documentation from the API if we are confident of it for the C++ wrapper:
// #GVariant is completely threadsafe.  A #GVariant instance can be
// concurrently accessed in any way from any number of threads without
// problems.
// Note that we don't copy GVariant's documentation about Memory Use because
// it seems easy to get out of sync and people can look at that C documentation if necessary.

/** This is the base class for all Variant types.
 *
 * If the actual type is known at compile-time then you should use a specific
 * Variant<>, such as Variant<int>. Otherwise, you may use get_type(),
 * is_of_type(), or cast_dynamic().
 *
 * @newin{2,28}
 * @ingroup Variant
 */
class GLIBMM_API VariantBase
{
  _CLASS_OPAQUE_COPYABLE(VariantBase, GVariant, NONE, g_variant_ref_sink, g_variant_unref, GLIBMM_API)
  _CUSTOM_CTOR_CAST()
  _IGNORE(g_variant_ref, g_variant_ref_sink, g_variant_take_ref, g_variant_unref,
    g_variant_get, g_variant_get_va)
public:

_DEPRECATE_IFDEF_START
  /** This typedef is just to make it more obvious that
   * our operator const void* should be used like operator bool().
   *
   * @deprecated Use the explicit operator bool() instead.
   */
  using BoolExpr = const void*;

  /** Test whether the Variant has an underlying instance.
   *
   * Mimics usage of pointers:
   * @code
   *   if (variant)
   *     do_something();
   * @endcode
   *
   * @deprecated Use the explicit operator bool() instead.
   *
   * @newin{2,36}
   */
   operator BoolExpr() const;
_DEPRECATE_IFDEF_END

   /** Test whether the Variant has an underlying instance.
    *
    * @newin{2,50}
    */
   explicit operator bool() const;

  /** Replace the underlying GVariant.
   * This is for use by methods that take a VariantBase& as an output
   * parameter.
   *
   * @param cobject The GVariant* obtained from a C function.
   * @param take_a_reference Whether this method should take a reference, for
   * instance if the C function has not given one.
   */
  void init(const GVariant* cobject, bool take_a_reference = false);

// It's necessary to take an extra reference of the 'const GVariantType*'
// returned by g_variant_get_type() because it doesn't do that already.
#m4 _CONVERSION(`const GVariantType*',`VariantType',`Glib::wrap(const_cast<GVariantType*>($3), true)')
  _WRAP_METHOD(VariantType get_type() const, g_variant_get_type)

  _WRAP_METHOD(std::string get_type_string() const, g_variant_get_type_string)
  _WRAP_METHOD(bool is_floating() const, g_variant_is_floating)
  _WRAP_METHOD(bool is_of_type(const VariantType& type) const, g_variant_is_of_type)
  _WRAP_METHOD(bool is_container() const, g_variant_is_container)
  _WRAP_METHOD(GVariantClass classify() const, g_variant_classify)

  _WRAP_METHOD(gsize get_size() const, g_variant_get_size)
  _WRAP_METHOD(gconstpointer get_data(), g_variant_get_data, deprecated "Use the const version instead.")
  _WRAP_METHOD(gconstpointer get_data() const, g_variant_get_data, newin "2,46")
  _WRAP_METHOD(Glib::RefPtr<const Glib::Bytes> get_data_as_bytes() const, g_variant_get_data_as_bytes, newin "2,46")
  _WRAP_METHOD(void store(gpointer data) const, g_variant_store)

  _WRAP_METHOD(Glib::ustring print(bool type_annotate = false) const, g_variant_print)
  _IGNORE(g_variant_print_string)

  #m4 _CONVERSION(`const VariantBase&',`gconstpointer',`const_cast<GVariant*>(($3).gobj())')
  _WRAP_METHOD(guint hash() const, g_variant_hash)

  /** Checks if @a *this and @a other have the same type and value.
   *
   * @newin{2,24}
   *
   * @param other The Variant to compare with.
   * @return <tt>true</tt> if @a *this and @a other are equal.
   */
  _WRAP_METHOD(bool equal(const VariantBase& other) const, g_variant_equal)

  /** Gets a VariantBase instance that has the same value as this variant and
   * is trusted to be in normal form.
   *
   * If this variant is already trusted to be in normal form then a new
   * reference to the variant is returned.
   *
   * If this variant is not already trusted, then it is scanned to check if it
   * is in normal form. If it is found to be in normal form then it is marked
   * as trusted and a new reference to it is returned.
   *
   * If this variant is found not to be in normal form then a new trusted
   * VariantBase is created with the same value as this variant.
   *
   * It makes sense to call this function if you've received variant data from
   * untrusted sources and you want to ensure your serialised output is
   * definitely in normal form.
   *
   * @param result A location in which to store the trusted VariantBase.
   * @newin{2,24}
   */
  void get_normal_form(VariantBase& result) const;
  _IGNORE(g_variant_get_normal_form)

  _WRAP_METHOD(bool is_normal_form() const, g_variant_is_normal_form)

  /** Performs a byteswapping operation on the contents of this variant. The
   * result is that all multi-byte numeric data contained in the variant is
   * byteswapped. That includes 16, 32, and 64bit signed and unsigned integers
   * as well as file handles and double precision floating point values.
   *
   * This function is an identity mapping on any value that does not contain
   * multi-byte numeric data. That include strings, booleans, bytes and
   * containers containing only these things (recursively).
   *
   * The returned value is always in normal form and is marked as trusted.
   *
   * @param result A location in which to store the byteswapped form of this
   * variant.
   * @newin{2,24}
   */
   void byteswap(VariantBase& result) const;
   _IGNORE(g_variant_byteswap)

   _WRAP_METHOD(bool check_format_string(const std::string& format_string, bool copy_only = false) const, g_variant_check_format_string)

   //Ignore private API from gvariant-core.h:
   _IGNORE(g_variant_is_trusted, g_variant_get_type_info)

   /** Cast to a specific variant type.
    * For instance:
    * @code
    * Variant<std::string> derived = VariantBase::cast_dynamic< Variant<std::string> >(base);
    * @endcode
    *
    * @param v The variant to cast to a specific type.
    * @result The variant as a specific type.
    * @throws std::bad_cast if the Variant was not of the expected type.
    */
   template<class V_CastTo>
   static V_CastTo cast_dynamic(const VariantBase& v);

   _IGNORE(g_variant_dict_new)

protected:
#ifndef DOXYGEN_SHOULD_SKIP_THIS
  /** Used by cast_dynamic().
   * In addition to an exact match, the following casts are possible:
   * - VARIANT_TYPE_OBJECT_PATH and VARIANT_TYPE_SIGNATURE can be cast to
   *   VARIANT_TYPE_STRING (Glib::ustring).
   * - VARIANT_TYPE_STRING, VARIANT_TYPE_OBJECT_PATH and VARIANT_TYPE_SIGNATURE
   *   can be cast to VARIANT_TYPE_BYTESTRING (std::string).
   * - VARIANT_TYPE_HANDLE can be cast to VARIANT_TYPE_INT32.
   *
   * These casts are possible also when they are parts of a more complicated type.
   * E.g. in Variant<std::map<Glib::ustring, std::vector<std::string> > > the map's keys
   * can be VARIANT_TYPE_OBJECT_PATH and the vector's elements can be VARIANT_TYPE_SIGNATURE.
   * @newin{2,46}
   */
  bool is_castable_to(const VariantType& supertype) const;
#endif //DOXYGEN_SHOULD_SKIP_THIS

private:
  /** Relational operators are deleted to prevent invalid conversion
   * to const void*.
   */
  bool operator<(const VariantBase& src) const;

  /// See operator<().
  bool operator<=(const VariantBase& src) const;

  /// See operator<().
  bool operator>(const VariantBase& src) const;

  /// See operator<().
  bool operator>=(const VariantBase& src) const;

  /// See operator<().
  bool operator==(const VariantBase& src) const;

  /// See operator<().
  bool operator!=(const VariantBase& src) const;
};

template<class V_CastTo>
V_CastTo VariantBase::cast_dynamic(const VariantBase& v)
{
  if(!(v.gobj()))
  {
    return V_CastTo();
  }
  if(v.is_castable_to(V_CastTo::variant_type()))
  {
    return V_CastTo(const_cast<GVariant*>(v.gobj()), true);
  }
  else
  {
   throw std::bad_cast();
  }
}

/** Base class from which string variant classes derive.
 * @newin{2,28}
 * @ingroup Variant
 */
class GLIBMM_API VariantStringBase : public VariantBase
{
  // Trick gmmproc into thinking this is derived from GVariant to wrap some methods.
  _CLASS_GENERIC(VariantStringBase, GVariant)

public:
  using CType = GVariant*;
  using CppType = VariantStringBase;

  /// Default constructor.
  VariantStringBase();

  /** GVariant constructor.
   * @param castitem The GVariant to wrap.
   * @param take_a_reference Whether to take an extra reference of the
   * GVariant or not (not taking one could destroy the GVariant with the
   * wrapper).
   */
  explicit VariantStringBase(GVariant* castitem,  bool take_a_reference = false);

  /** Creates a D-Bus object path variant with the contents of @a object_path.
   * @a object_path must be a valid D-Bus object path. Use is_object_path() if unsure.
   *
   * @param[out] output A location in which to store the new object path variant
   * instance.
   * @param object_path An object path string.
   * @newin{2,28}
   */
  static void create_object_path(VariantStringBase& output,
    const std::string& object_path);
  _IGNORE(g_variant_new_object_path)

  _WRAP_METHOD(static bool is_object_path(const std::string& string), g_variant_is_object_path)

  /** Creates a D-Bus type signature variant with the contents of @a signature.
   * @a signature must be a valid D-Bus type signature. Use is_signature() if unsure.
   *
   * @param[out] output A location in which to store the new signature variant
   * instance.
   * @param signature A signature string.
   * @newin{2,28}
   */
  static void create_signature(VariantStringBase& output,
    const std::string& signature);
  _IGNORE(g_variant_new_signature)

  _WRAP_METHOD(static bool is_signature(const std::string& string), g_variant_is_signature)
};

/** The base class for multiple-item Variants, such as Variants containing
 * tuples or arrays, and also for maybe-typed (that is, nullable) Variant types.
 *
 * @newin{2,28}
 * @ingroup Variant
 */
class GLIBMM_API VariantContainerBase : public VariantBase
{
  // Trick gmmproc into thinking this is derived from GVariant to wrap some methods.
  _CLASS_GENERIC(VariantContainerBase, GVariant)

public:
  using CType = GVariant*;
  using CppType = VariantContainerBase;

  /// Default constructor.
  VariantContainerBase();

  /** GVariant constructor.
   * @param castitem The GVariant to wrap.
   * @param take_a_reference Whether to take an extra reference of the
   * GVariant or not (not taking one could destroy the GVariant with the
   * wrapper).
   */
  explicit VariantContainerBase(GVariant* castitem, bool take_a_reference = false);

  /** Create a tuple variant from a vector of its variant children.
   * @param children The vector containing the children of the container.
   * @return The newly created tuple variant (as a VariantContainerBase).
   */
  static VariantContainerBase create_tuple(const std::vector<VariantBase>& children);

  /** Create a tuple variant with a single variant child.
   * @param child The child variant.
   * @return The newly created tuple variant (as a VariantContainerBase).
   */
  static VariantContainerBase create_tuple(const VariantBase& child);

  _WRAP_METHOD_DOCS_ONLY(g_variant_new_maybe)
  static VariantContainerBase create_maybe(const VariantType& child_type,
    const VariantBase& child = VariantBase());

  _WRAP_METHOD(gsize get_n_children() const, g_variant_n_children)

  /** Reads a child item out of this instance. This method is valid for
   * variants, maybes, arrays, tuples and dictionary entries.
   *
   * It is an error if @a index is greater than the number of child items in
   * the container. See get_n_children().
   *
   * This function is O(1).
   *
   * @param index The index of the child to fetch.
   * @param child A location in which to store the child at the specified
   * index.
   * @throw std::out_of_range
   * @newin{2,28}
   */
  void get_child(VariantBase& child, gsize index = 0) const;
  _IGNORE(g_variant_get_child, g_variant_get_child_value)

#m4 _CONVERSION(`GVariant*',`VariantBase',`Glib::wrap($3)')

  _WRAP_METHOD(VariantBase get_child(gsize index = 0), g_variant_get_child_value)

  /* TODO?:
  /// A get() method to return the contents of the variant in the container.
  template <class DataType>
  DataType get_child(gsize index = 0) const;
  */

  /** If this is a maybe-typed instance, try to extract its value. If there is
   * no value (the value is <tt>nothing</tt>), return <tt>false</tt>. Otherwise,
   * the value is copied to the supplied Variant and <tt>true</tt> is returned.
   *
   * @param maybe A place in which to return the value, if it isn’t
   * <tt>nothing</tt>.
   * @newin{2,28}
   */
  bool get_maybe(VariantBase& maybe) const;
  _IGNORE(g_variant_get_maybe)

protected:
#ifndef DOXYGEN_SHOULD_SKIP_THIS
  /** Used by get_iter() in the subclasses.
   * @newin{2,46}
   */
  VariantIter get_iter(const VariantType& container_variant_type) const;
#endif //DOXYGEN_SHOULD_SKIP_THIS
};

template<>
GLIBMM_API VariantContainerBase VariantBase::cast_dynamic<VariantContainerBase>(const VariantBase& v);

/** Template class used for the specialization of the Variant<> classes.
 * @newin{2,28}
 * @ingroup Variant
 */
template<class T>
class Variant : public VariantBase
{
public:
  using CppType = T;
};

/****************** Specializations ***********************************/

/** Specialization of Variant containing a VariantBase.
 * Perhaps the main use of this is as a maybe-typed (i.e. nullable) Variant, as
 * it inherits the methods create_maybe() and get_maybe() from
 * VariantContainerBase, plus get_n_children() to allow checking whether there
 * is a contained value, i.e. the inner Variant is not <tt>nothing</tt>.
 *
 * @newin{2,28}
 * @ingroup Variant
 */
template<>
class GLIBMM_API Variant<VariantBase> : public VariantContainerBase
{
  // Trick gmmproc into thinking this is derived from GVariant to wrap some methods.
  _CLASS_GENERIC(Variant<VariantBase>, GVariant)

public:
  using CType = GVariant*;
  using CppType = VariantBase;
  using CppContainerType = Variant<VariantBase>;

  /// Default constructor.
  Variant<VariantBase>();

  /** GVariant constructor.
   * @param castitem The GVariant to wrap.
   * @param take_a_reference Whether to take an extra reference of the
   * GVariant or not (not taking one could destroy the GVariant with the
   * wrapper).
   */
  explicit Variant<VariantBase>(GVariant* castitem, bool take_a_reference = false);

  /** Gets the VariantType.
   * @return The VariantType.
   * @newin{2,28}
   */
  static const VariantType& variant_type() G_GNUC_CONST;

  //This must have a create() method because otherwise it would be a copy
  //constructor.
  /** Creates a new Variant<VariantBase>.
   * @param data The value of the new Variant.
   * @return The new Variant.
   * @newin{2,28}
   */
  static Variant<VariantBase> create(const VariantBase& data);
  _IGNORE(g_variant_new_variant)

  //TODO: Documentation
  void get(VariantBase& variant) const;

  //TODO: Deprecate this in favour of get(VariantBase&)?
  _WRAP_METHOD(VariantBase get() const, g_variant_get_variant)
};

/** Specialization of Variant containing a Variant<T>.
 * Perhaps the main use of this is as a maybe-typed (i.e. nullable) Variant, as
 * it inherits the methods create_maybe() and get_maybe() from
 * VariantContainerBase, plus get_n_children() to allow checking whether there
 * is a contained value, i.e. the inner Variant is not <tt>nothing</tt>.
 *
 * @newin{2,36}
 * @ingroup Variant
 */
template<class T>
class Variant< Variant<T> > : public VariantContainerBase
{
public:
  using CType = GVariant*;
  using CppType = Variant<T>;
  using CppContainerType = Variant<CppType>;

  /// Default constructor.
  Variant< Variant<T> >();

  /** GVariant constructor.
   * @param castitem The GVariant to wrap.
   * @param take_a_reference Whether to take an extra reference of the
   * GVariant or not (not taking one could destroy the GVariant with the
   * wrapper).
   * @newin{2,36}
   */
  explicit Variant< Variant<T> >(GVariant* castitem, bool take_a_reference = false);

  /** Gets the VariantType.
   * @return The VariantType.
   * @newin{2,36}
   */
  static const VariantType& variant_type() G_GNUC_CONST;

  /** Creates a new Variant< Variant<T> >.
   * @param data The value of the new Variant.
   * @return The new Variant.
   * @newin{2,36}
   */
  static Variant< Variant<T> > create(const Variant<T>& data);

  /** Gets the contents of the Variant.
   * @return The contents of the Variant.
   * @newin{2,36}
   */
  Variant<T> get() const;
};

/** Specialization of Variant containing a Glib::ustring, for variants of type
 * string, object path, or signature.
 * @newin{2,28}
 * @ingroup Variant
 */
template<>
class GLIBMM_API Variant<Glib::ustring> : public VariantStringBase
{
  // Trick gmmproc into thinking this is derived from GVariant to wrap some methods.
  _CLASS_GENERIC(Variant<Glib::ustring>, GVariant)
public:
  using CType = char*;
  using CppType = Glib::ustring;

  /// Default constructor.
  Variant<Glib::ustring>();

  /** GVariant constructor.
   * @param castitem The GVariant to wrap.
   * @param take_a_reference Whether to take an extra reference of the
   * GVariant or not (not taking one could destroy the GVariant with the
   * wrapper).
   */
  explicit Variant<Glib::ustring>(GVariant* castitem,  bool take_a_reference = false);

  /** Gets the VariantType.
   * @return The VariantType.
   * @newin{2,28}
   */
  static const VariantType& variant_type() G_GNUC_CONST;

  /** Creates a new Variant<Glib::ustring>.
   * @param data The value of the new Variant.
   * @return The new Variant.
   * @newin{2,28}
   */
  static Variant<Glib::ustring> create(const Glib::ustring& data);

  //We can't use WRAP_METHOD() here because g_variant_get_string() takes an extra length parameter.
  /** Gets the contents of the Variant.
   * @return The contents of the Variant.
   * @newin{2,28}
   */
  Glib::ustring get() const;
  _IGNORE(g_variant_get_string, g_variant_dup_string)
};

//TODO: When we can break ABI, remove this template specialization.
template<>
GLIBMM_API Variant<Glib::ustring> VariantBase::cast_dynamic< Variant<Glib::ustring> >(const VariantBase& v);

/** Specialization of Variant containing a Glib::DBusObjectPathString,
 * for variants of type object path.
 * @newin{2,54}
 * @ingroup Variant
 */
template<>
class GLIBMM_API Variant<Glib::DBusObjectPathString> : public VariantStringBase
{
  // Trick gmmproc into thinking this is derived from GVariant to wrap some methods.
  _CLASS_GENERIC(Variant<Glib::DBusObjectPathString>, GVariant)
public:
  using CType = char*;
  using CppType = Glib::DBusObjectPathString;

  /// Default constructor.
  Variant();

  /** GVariant constructor.
   * @param castitem The GVariant to wrap.
   * @param take_a_reference Whether to take an extra reference of the
   * GVariant or not (not taking one could destroy the GVariant with the
   * wrapper).
   */
  explicit Variant(GVariant* castitem,  bool take_a_reference = false);

  /** Gets the VariantType.
   * @return The VariantType.
   * @newin{2,54}
   */
  static const VariantType& variant_type() G_GNUC_CONST;

  /** Creates a new Variant<Glib::DBusObjectPathString>.
   * @param data The value of the new Variant.
   * @return The new Variant.
   * @newin{2,54}
   */
  static Variant<CppType> create(const CppType& data);

  //We can't use WRAP_METHOD() here because g_variant_get_string() takes an extra length parameter.
  /** Gets the contents of the Variant.
   * @return The contents of the Variant.
   * @newin{2,54}
   */
  CppType get() const;
};

/** Specialization of Variant containing a Glib::DBusSignatureString,
 * for variants of type signature.
 * @newin{2,54}
 * @ingroup Variant
 */
template<>
class GLIBMM_API Variant<Glib::DBusSignatureString> : public VariantStringBase
{
  // Trick gmmproc into thinking this is derived from GVariant to wrap some methods.
  _CLASS_GENERIC(Variant<Glib::DBusSignatureString>, GVariant)
public:
  using CType = char*;
  using CppType = Glib::DBusSignatureString;

  /// Default constructor.
  Variant();

  /** GVariant constructor.
   * @param castitem The GVariant to wrap.
   * @param take_a_reference Whether to take an extra reference of the
   * GVariant or not (not taking one could destroy the GVariant with the
   * wrapper).
   */
  explicit Variant(GVariant* castitem,  bool take_a_reference = false);

  /** Gets the VariantType.
   * @return The VariantType.
   * @newin{2,54}
   */
  static const VariantType& variant_type() G_GNUC_CONST;

  /** Creates a new Variant<Glib::DBusSignatureString>.
   * @param data The value of the new Variant.
   * @return The new Variant.
   * @newin{2,54}
   */
  static Variant<CppType> create(const CppType& data);

  //We can't use WRAP_METHOD() here because g_variant_get_string() takes an extra length parameter.
  /** Gets the contents of the Variant.
   * @return The contents of the Variant.
   * @newin{2,54}
   */
  CppType get() const;
};

/** Specialization of Variant containing a std::string, for variants of type
 * bytestring, string, object path, or signature.
 * See also Variant<Glib::ustring> for UTF-8 strings.
 * @newin{2,28}
 * @ingroup Variant
 */
template<>
class GLIBMM_API Variant<std::string> : public VariantStringBase
{
  // Trick gmmproc into thinking this is derived from GVariant to wrap some methods.
  _CLASS_GENERIC(Variant<std::string>, GVariant)
public:
  using CType = char*                ;
  using CppType = std::string;

  /// Default constructor.
  Variant<std::string>();

  /** GVariant constructor.
   * @param castitem The GVariant to wrap.
   * @param take_a_reference Whether to take an extra reference of the
   * GVariant or not (not taking one could destroy the GVariant with the
   * wrapper).
   */
  explicit Variant<std::string>(GVariant* castitem, bool take_a_reference = false);

  /** Gets the VariantType.
   * @return The VariantType.
   * @newin{2,28}
   */
  static const VariantType& variant_type() G_GNUC_CONST;

  /** Creates a new Variant<std::string>.
   * @param data The value of the new Variant.
   * @return The new Variant.
   * @newin{2,28}
   */
  static Variant<std::string> create(const std::string& data);

  //TODO: Documentation.
  std::string get() const;
  _IGNORE(g_variant_get_bytestring, g_variant_dup_bytestring)
};

//TODO: When we can break ABI, remove this template specialization.
template<>
GLIBMM_API Variant<std::string> VariantBase::cast_dynamic< Variant<std::string> >(const VariantBase& v);

/** Specialization of Variant containing a dictionary entry.  See also
 * Variant< std::map<K, V> >.
 * @newin{2,28}
 * @ingroup Variant
 */
template<class K, class V>
class Variant< std::pair<K, V> > : public VariantContainerBase
{
public:
  using CppType = std::pair<K, V>;
  using CppContainerType = Variant<CppType>;

  /// Default constructor.
  Variant< std::pair<K, V> >()
  : VariantContainerBase()
  {}

  /** GVariant constructor.
   * @param castitem The GVariant to wrap.
   * @param take_a_reference Whether to take an extra reference of the
   * GVariant or not (not taking one could destroy the GVariant with the
   * wrapper).
   */
  explicit Variant< std::pair<K, V> >(GVariant* castitem,
    bool take_a_reference = false)
  : VariantContainerBase(castitem, take_a_reference)
  {}

  /** Gets the VariantType.
   * @return The VariantType.
   * @newin{2,28}
   */
  static const VariantType& variant_type() G_GNUC_CONST;

  /** Creates a new Variant< std::pair<K, V> >.
   * @param data The value of the new Variant.
   * @return The new Variant.
   * @newin{2,28}
   */
  static Variant< std::pair<K, V> > create(const std::pair<K, V>& data);
  _IGNORE(g_variant_new_dict_entry)

  /** Gets the contents of the Variant.
   * @return The contents of the Variant.
   * @throw std::out_of_range
   * @newin{2,28}
   */
  std::pair<K, V> get() const;
};

/** Specialization of Variant containing an array of items.
 * @newin{2,28}
 * @ingroup Variant
 */
template<class T>
class Variant< std::vector<T> > : public VariantContainerBase
{
public:
  using CppType = T                    ;
  using CppContainerType = std::vector<T>;

  /// Default constructor.
  Variant< std::vector<T> >()
  : VariantContainerBase()
  {}

  /** GVariant constructor.
   * @param castitem The GVariant to wrap.
   * @param take_a_reference Whether to take an extra reference of the
   * GVariant or not (not taking one could destroy the GVariant with the
   * wrapper).
   */
  explicit Variant< std::vector<T> >(GVariant* castitem,
    bool take_a_reference = false)
  : VariantContainerBase(castitem, take_a_reference)
  {}

  /** Gets the VariantType.
   * @return The VariantType.
   * @newin{2,28}
   */
  static const VariantType& variant_type() G_GNUC_CONST;

  /** Creates a new Variant from an array of numeric types.
   * @param data The array to use for creation.
   * @return The new Variant.
   * @newin{2,28}
   */
  static Variant< std::vector<T> > create(const std::vector<T>& data);
  _IGNORE(g_variant_new_array)

  /** Gets a specific element of the array.  It is an error if @a index is
   * greater than the number of child items in the container.  See
   * VariantContainerBase::get_n_children().
   *
   * This function is O(1).
   *
   * @param index The index of the element.
   * @return The element at index @a index.
   * @throw std::out_of_range
   * @newin{2,28}
   */
  T get_child(gsize index) const;

  /** Gets the vector of the Variant.
   * @return The vector.
   * @newin{2,28}
   */
  std::vector<T> get() const;
  _IGNORE(g_variant_get_fixed_array)

  /** Gets a VariantIter of the Variant.
   * @return the VariantIter.
   * @newin{2,28}
   */
  VariantIter get_iter() const;
};

/** Specialization of Variant containing an array of UTF-8 capable
 * strings.
 * @newin{2,28}
 * @ingroup Variant
 */
template<>
class GLIBMM_API Variant< std::vector<Glib::ustring> > : public VariantContainerBase
{
public:
  using CppType = Glib::ustring                ;
  using CppContainerType = std::vector<Glib::ustring>;

  /// Default constructor.
  Variant< std::vector<Glib::ustring> >();

  /** GVariant constructor.
   * @param castitem The GVariant to wrap.
   * @param take_a_reference Whether to take an extra reference of the
   * GVariant or not (not taking one could destroy the GVariant with the
   * wrapper).
   */
  explicit Variant< std::vector<Glib::ustring> >(GVariant* castitem, bool take_a_reference = false);

  /** Gets the VariantType.
   * @return The VariantType.
   * @newin{2,28}
   */
  static const VariantType& variant_type() G_GNUC_CONST;

  /** Creates a new Variant from an array of strings.
   * @param data The array to use for creation.
   * @return The new Variant.
   * @newin{2,28}
   */
  static Variant< std::vector<Glib::ustring> >
    create(const std::vector<Glib::ustring>& data);

  /** Gets a specific element of the string array.  It is an error if @a index
   * is greater than the number of child items in the container.  See
   * VariantContainerBase::get_n_children().
   *
   * This function is O(1).
   *
   * @param index The index of the element.
   * @return The element at index @a index.
   * @throw std::out_of_range
   * @newin{2,28}
   */
  Glib::ustring get_child(gsize index) const;

  /** Gets the string vector of the Variant.
   * @return The vector.
   * @newin{2,28}
   */
  std::vector<Glib::ustring> get() const;
  _IGNORE(g_variant_get_strv, g_variant_dup_strv)

  /** Gets a VariantIter of the Variant.
   * @return the VariantIter.
   * @newin{2,28}
   */
  VariantIter get_iter() const;
};

/** Specialization of Variant containing an array of D-Bus object paths.
 *
 * @newin{2,54}
 * @ingroup Variant
 */
template<>
class GLIBMM_API Variant<std::vector<Glib::DBusObjectPathString>> : public VariantContainerBase
{
public:
  using CppType = Glib::DBusObjectPathString;
  using CppContainerType = std::vector<Glib::DBusObjectPathString>;

  /// Default constructor.
  Variant();

  /** GVariant constructor.
   * @param castitem The GVariant to wrap.
   * @param take_a_reference Whether to take an extra reference of the
   * GVariant or not (not taking one could destroy the GVariant with the
   * wrapper).
   */
  explicit Variant(GVariant* castitem, bool take_a_reference = false);

  /** Gets the VariantType.
   * @return The VariantType.
   * @newin{2,54}
   */
  static const VariantType& variant_type() G_GNUC_CONST;

  /** Creates a new Variant from an array of strings.
   * @param data The array to use for creation.
   * @return The new Variant.
   * @newin{2,54}
   */
  static Variant<CppContainerType> create(const CppContainerType& data);

  /** Gets a specific element of the string array.  It is an error if @a index
   * is greater than the number of child items in the container.  See
   * VariantContainerBase::get_n_children().
   *
   * This function is O(1).
   *
   * @param index The index of the element.
   * @return The element at index @a index.
   * @throw std::out_of_range
   * @newin{2,54}
   */
  CppType get_child(gsize index) const;

  /** Gets the string vector of the Variant.
   * @return The vector.
   * @newin{2,54}
   */
  CppContainerType get() const;

  /** Gets a VariantIter of the Variant.
   * @return the VariantIter.
   * @newin{2,54}
   */
  VariantIter get_iter() const;
};

/** Specialization of Variant containing an array of non-UTF-8 strings
 * (byte string arrays).
 * @newin{2,28}
 * @ingroup Variant
 */
template<>
class GLIBMM_API Variant< std::vector<std::string> > : public VariantContainerBase
{
public:
  using CppType = std::string                  ;
  using CppContainerType = std::vector<std::string>;

  /// Default constructor.
  Variant< std::vector<std::string> >();

  /** GVariant constructor.
   * @param castitem The GVariant to wrap.
   * @param take_a_reference Whether to take an extra reference of the
   * GVariant or not (not taking one could destroy the GVariant with the
   * wrapper).
   */
  explicit Variant< std::vector<std::string> >(GVariant* castitem, bool take_a_reference = false);

  /** Gets the VariantType.
   * @return The VariantType.
   * @newin{2,28}
   */
  static const VariantType& variant_type() G_GNUC_CONST;

  /** Creates a new Variant from an array of strings.
   * @param data The array to use for creation.
   * @return The new Variant.
   * @newin{2,28}
   */
  static Variant< std::vector<std::string> >
    create(const std::vector<std::string>& data);

  /** Creates a new Variant from an array of D-Bus object paths.
   * @param paths The array to use for creation.
   * @return The new Variant.
   * @newin{2,36}
   */
  static Variant< std::vector<std::string> >
    create_from_object_paths(const std::vector<std::string>& paths);

  /** Gets a specific element of the string array.  It is an error if @a index
   * is greater than the number of child items in the container.  See
   * VariantContainerBase::get_n_children().
   *
   * This function is O(1).
   *
   * @param index The index of the element.
   * @return The element at index @a index.
   * @throw std::out_of_range
   * @newin{2,28}
   */
  std::string get_child(gsize index) const;

  /** Gets the string vector of the Variant.
   * @return The vector.
   * @newin{2,28}
   */
  std::vector<std::string> get() const;
  _IGNORE(g_variant_get_bytestring_array, g_variant_dup_bytestring_array)

  // Object paths are merely strings so it is possible to get them already with
  // the existing get() methods in this class.
  _IGNORE(g_variant_get_objv, g_variant_dup_objv)

  /** Gets a VariantIter of the Variant.
   * @return the VariantIter.
   * @newin{2,28}
   */
  VariantIter get_iter() const;
};

/** Specialization of Variant containing a dictionary (a map of (key,
 * value) elements).
 * @newin{2,28}
 * @ingroup Variant
 */
template<class K, class V>
class Variant< std::map<K, V> >: public VariantContainerBase
{
public:
  using CppType = std::pair<K, V>;
  using CppContainerType = std::map<K, V>;

  /// Default constructor.
  Variant< std::map<K, V> >()
  : VariantContainerBase()
  {}

  /** GVariant constructor.
   * @param castitem The GVariant to wrap.
   * @param take_a_reference Whether to take an extra reference of the
   * GVariant or not (not taking one could destroy the GVariant with the
   * wrapper).
   */
  explicit Variant< std::map<K, V> >(GVariant* castitem,
    bool take_a_reference = false)
  : VariantContainerBase(castitem, take_a_reference)
  {}

  /** Gets the VariantType.
   * @return The VariantType.
   * @newin{2,28}
   */
  static const VariantType& variant_type() G_GNUC_CONST;

  /** Creates a new Variant containing a dictionary from a map.
   * @param data The map to use for creation.
   * @return The new Variant holding a dictionary.
   * @newin{2,28}
   */
  static Variant< std::map<K, V> > create(const std::map<K, V>& data);

  /** Gets a specific dictionary entry from the string array.  It is an error
   * if @a index is greater than the number of child items in the container.
   * See VariantContainerBase::get_n_children().
   *
   * This function is O(1).
   *
   * @param index The index of the element.
   * @return The dictionary entry at index @a index.
   * @throw std::out_of_range
   * @newin{2,28}
   */
  std::pair<K, V> get_child(gsize index) const;

  /** Looks up a value in a dictionary Variant.
   * @param key The key to look up.
   * @param value A location in which to store the value if found.
   * @return <tt>true</tt> if the key is found, <tt>false</tt> otherwise.
   */
  bool lookup(const K& key, V& value) const;
  _IGNORE(g_variant_lookup_value, g_variant_lookup)

  /** Gets the map (the dictionary) of the Variant.
   * @return The vector.
   * @newin{2,28}
   */
  std::map<K, V> get() const;

  /** Gets a VariantIter of the Variant.
   * @return the VariantIter.
   * @newin{2,28}
   */
  VariantIter get_iter() const;
};

/** Specialization of Variant containing a tuple.
 * @newin{2,54}
 * @ingroup Variant
 */
template <class... Types>
class Variant<std::tuple<Types...>> : public VariantContainerBase
{
public:
  using CppContainerType = std::tuple<Types...>;

  /// Default constructor
  Variant<std::tuple<Types...>>()
  : VariantContainerBase()
  {}

  /** GVariant constructor.
   * @param castitem The GVariant to wrap.
   * @param take_a_reference Whether to take an extra reference of the GVariant
   *        or not (not taking one could destroy the GVariant with the wrapper).
   */
  explicit Variant<std::tuple<Types...>>(GVariant* castitem, bool take_a_reference = false)
  : VariantContainerBase(castitem, take_a_reference)
  {}

  /** Creates a new Variant containing a tuple.
   * @param data The tuple to use for creation.
   * @return The new Variant holding a tuple.
   * @newin{2,54}
   */
  static Variant<std::tuple<Types...>> create(const std::tuple<Types...>& data);

  /** Gets the VariantType.
   * @return The VariantType.
   * @newin{2,54}
   */
  static const VariantType& variant_type() G_GNUC_CONST;

  /** Gets a specific element from the tuple.
   * It is an error if @a index is greater than or equal to the number of
   * elements in the tuple. See VariantContainerBase::get_n_children().
   *
   * @param index The index of the element.
   * @return The tuple element at index @a index.
   * @throw std::out_of_range
   * @newin{2,54}
   */
  template<class T>
  T get_child(gsize index) const;

  template<class T>
  Variant<T> get_child_variant(gsize index) const;

  /** Gets the tuple of the Variant.
   * @return The tuple.
   * @newin{2,54}
   */
  std::tuple<Types...> get() const;

  /** Gets a VariantIter of the Variant.
   * @return The VariantIter.
   * @newin{2,54}
   */
  VariantIter get_iter() const;
};

} // namespace Glib


//We ignore g_variant_get_*() methods that are wrapped by Variant<> specializations, such as in variant_basictypes.h.m4.
_IGNORE(
  g_variant_get_boolean,
  g_variant_get_byte,
  g_variant_get_int16,
  g_variant_get_uint16,
  g_variant_get_int32,
  g_variant_get_handle,
  g_variant_get_uint32,
  g_variant_get_int64,
  g_variant_get_uint64,
  g_variant_get_double,
  g_variant_iter_new
)

/* Include generated specializations of Variant<> for fundamental types:
 */
#define _GLIBMM_VARIANT_H_INCLUDE_VARIANT_BASICTYPES_H
#include <glibmm/variant_basictypes.h>
#undef _GLIBMM_VARIANT_H_INCLUDE_VARIANT_BASICTYPES_H

namespace Glib
{

/*--------------------Variant< Variant<T> >---------------------*/

template<class T>
Variant< Variant<T> >::Variant()
: VariantContainerBase()
{
}

template<class T>
Variant< Variant<T> >::Variant(GVariant* castitem, bool take_a_reference)
: VariantContainerBase(castitem, take_a_reference)
{
}

// static
template<class T>
const VariantType& Variant< Variant<T> >::variant_type()
{
  return VARIANT_TYPE_VARIANT;
}

template<class T>
Variant< Variant<T> > Variant< Variant<T> >::create(const Variant<T>& data)
{
  Variant< Variant<T> > result = Variant< Variant<T> >(
    g_variant_new_variant(const_cast<GVariant*>(data.gobj())));
  return result;
}

template<class T>
Variant<T> Variant< Variant<T> >::get() const
{
  GVariant* const gvariant = g_variant_get_variant(gobject_);
  return Variant<T>(gvariant);
}

/*--------------------Variant< std::pair<K, V> >---------------------*/

// static
template<class K, class V>
const VariantType& Variant< std::pair<K, V> >::variant_type()
{
  static VariantType type(
    g_variant_type_new_dict_entry(Variant<K>::variant_type().gobj(),
    Variant<V>::variant_type().gobj()));

  return type;
}

template<class K, class V>
Variant< std::pair<K, V> >
Variant< std::pair<K, V> >::create(const std::pair<K, V>& data)
{
  Variant<K> key = Variant<K>::create(data.first);
  Variant<V> value = Variant<V>::create(data.second);

  Variant< std::pair<K, V> > result = Variant< std::pair<K, V> >(
    g_variant_new_dict_entry(key.gobj(), value.gobj()));

  return result;
}

template<class K, class V>
std::pair<K, V> Variant< std::pair<K, V> >::get() const
{
  // Get the key (the first element of this VariantContainerBase).
  Variant<K> key;
  VariantContainerBase::get_child(key, 0);

  // Get the value (the second element of this VariantContainerBase).
  Variant<V> value;
  VariantContainerBase::get_child(value, 1);

  std::pair<K, V> result(key.get(), value.get());

  return result;
}

/*---------------------Variant< std::vector<T> >---------------------*/

// static
template<class T>
const VariantType& Variant< std::vector<T> >::variant_type()
{
  static VariantType type =
    VariantType::create_array(Variant<T>::variant_type());

  return type;
}

template<class T>
Variant< std::vector<T> >
Variant< std::vector<T> >::create(const std::vector<T>& data)
{
  // Get the variant type of the array.
  VariantType array_variant_type = Variant< std::vector<T> >::variant_type();

  // Create a GVariantBuilder to build the array.
  GVariantBuilder* builder = g_variant_builder_new(array_variant_type.gobj());

  // Add the elements of the vector into the builder.
  for(const auto& element : data)
  {
    Glib::Variant<T> variant = Glib::Variant<T>::create(element);
    g_variant_builder_add_value(builder, variant.gobj());
  }

  // Create the variant using the builder.
  Variant< std::vector<T> > result =
    Variant< std::vector<T> >(g_variant_new(
      reinterpret_cast<const gchar*>(array_variant_type.gobj()), builder));

  g_variant_builder_unref(builder);

  return result;
}

template<class T>
T Variant< std::vector<T> >::get_child(gsize index) const
{
  if (index >= get_n_children())
    throw std::out_of_range(
      "Variant< std::vector<T> >::get_child(): Index out of bounds.");

  Glib::Variant<T> variant;

  GVariant* gvariant =
    g_variant_get_child_value(const_cast<GVariant*>(gobj()), index);

  variant.init(gvariant);
  return variant.get();
}

template<class T>
std::vector<T> Variant< std::vector<T> >::get() const
{
  std::vector<T> result;

  for (gsize i = 0, n_children = get_n_children(); i < n_children; ++i)
  {
    Glib::Variant<T> variant;

    GVariant* gvariant =
      g_variant_get_child_value(const_cast<GVariant*>(gobj()), i);

    variant.init(gvariant);
    result.emplace_back(variant.get());
  }

  return result;
}

template<class T>
VariantIter Variant< std::vector<T> >::get_iter() const
{
  return VariantContainerBase::get_iter(variant_type());
}

/*---------------------Variant< std::map<K, V> > --------------------*/

// static
template<class K, class V>
const VariantType& Variant< std::map<K, V> >::variant_type()
{
  static VariantType type =
    VariantType::create_array(Variant< std::pair<K, V> >::variant_type());

  return type;
}

template<class K, class V>
Variant< std::map<K, V> >
Variant< std::map<K, V> >::create(const std::map<K, V>& data)
{
  // Get the variant type of the elements.
  VariantType element_variant_type =
    Variant< std::pair<K, V> >::variant_type();

  // Get the variant type of the array.
  VariantType array_variant_type = Variant< std::map<K, V> >::variant_type();

  // Create a GVariantBuilder to build the array.
  GVariantBuilder* builder = g_variant_builder_new(array_variant_type.gobj());

  // Add the elements of the map into the builder.
  for(const auto& element : data)
  {
    auto dict_entry =
      Variant< std::pair<K, V> >::create(element);

    g_variant_builder_add_value(builder, dict_entry.gobj());
  }

  // Create the variant using the builder.
  Variant< std::map<K, V> > result = Variant< std::map<K, V> >(g_variant_new(
    reinterpret_cast<const gchar*>(array_variant_type.gobj()), builder));

  g_variant_builder_unref(builder);

  return result;
}

template<class K, class V>
std::pair<K, V>
Variant< std::map<K, V> >::get_child(gsize index) const
{
  Variant< std::pair<K, V> > dict_entry;
  VariantContainerBase::get_child(dict_entry, index);
  return dict_entry.get();
}

template<class K, class V>
bool Variant< std::map<K, V> >::lookup(const K& key, V& value) const
{
  // The code in this method pretty much reflects the g_variant_lookup_value()
  // function except that it's more general to deal with keys that are not
  // just strings.
  VariantIter iter = get_iter();

  Variant< std::pair<K, V> > entry;

  while(iter.next_value(entry))
  {
    std::pair<K, V> element = entry.get();

    if(element.first == key)
    {
      value = element.second;
      return true;
    }
  }

  return false;
}

template<class K, class V>
std::map<K, V> Variant< std::map<K, V> >::get() const
{
  std::map<K, V> result;
  VariantIter iter = get_iter();
  Variant< std::pair<K, V> > entry;

  while(iter.next_value(entry))
  {
    result.insert(entry.get());
  }

  return result;
}

template<class K, class V>
VariantIter Variant< std::map<K, V> >::get_iter() const
{
  return VariantContainerBase::get_iter(variant_type());
}

/*---------------------Variant<std::tuple<class... Types>> --------------------*/

// static
template <class... Types>
const VariantType& Variant<std::tuple<Types...>>::variant_type()
{
  std::vector<VariantType> types;
  auto expander = [&types](const VariantType &type) mutable -> int
  {
    types.push_back(type);
    return 0;
  };

  // expands the variadic template parameters
  using swallow = int[]; // ensures left to right order
  (void)swallow{(expander(Variant<Types>::variant_type()))...};
  static auto type = VariantType::create_tuple(types);

  return type;
}

#ifndef DOXYGEN_SHOULD_SKIP_THIS
namespace detail
{
// std::index_sequence and std::index_sequence_for are new in C++14,
// but this version of glibmm requires only C++11.
// The following code replaces std::index_sequence and std::index_sequence_for
// until we can require C++14 support.
// See https://bugzilla.gnome.org/show_bug.cgi?id=787648

  /// Class template integer_sequence
  template<typename T, T... Idx>
    struct integer_sequence
    {
      typedef T value_type;
      static constexpr std::size_t size() { return sizeof...(Idx); }
    };

  // Concatenates two integer_sequences.
  template<typename Iseq1, typename Iseq2> struct iseq_cat;

  template<typename T, std::size_t... Ind1, std::size_t... Ind2>
    struct iseq_cat<integer_sequence<T, Ind1...>, integer_sequence<T, Ind2...>>
    {
      using type = integer_sequence<T, Ind1..., (Ind2 + sizeof...(Ind1))...>;
    };

  // Builds an integer_sequence<T, 0, 1, 2, ..., Num-1>.
  template<typename T, std::size_t Num>
    struct make_intseq
    : iseq_cat<typename make_intseq<T, Num / 2>::type,
		typename make_intseq<T, Num - Num / 2>::type>
    { };

  template<typename T>
    struct make_intseq<T, 1>
    {
      typedef integer_sequence<T, 0> type;
    };

  template<typename T>
    struct make_intseq<T, 0>
    {
      typedef integer_sequence<T> type;
    };

  /// Alias template make_integer_sequence
  template<typename T, T Num>
    using make_integer_sequence = typename make_intseq<T, Num>::type;

  /// Alias template index_sequence
  template<std::size_t... Idx>
    using index_sequence = integer_sequence<std::size_t, Idx...>;

  /// Alias template make_index_sequence
  template<std::size_t Num>
    using make_index_sequence = make_integer_sequence<std::size_t, Num>;

  /// Alias template index_sequence_for
  template<typename... Types>
    using index_sequence_for = make_index_sequence<sizeof...(Types)>;

// End of code that replaces std::index_sequence and std::index_sequence_for

template <class Tuple, std::size_t... Is>
void expand_tuple(std::vector<VariantBase> &variants, const Tuple & t,
                  detail::index_sequence<Is...>)
{
  using swallow = int[]; // ensures left to right order
  auto expander = [&variants](const VariantBase &variant) -> int
  {
    variants.push_back(variant);
    return 0;
  };
  (void)swallow {(expander(Variant<typename std::tuple_element<Is, Tuple>::type>::create(std::get<Is>(t))))...};
}
} // namespace detail
#endif // DOXYGEN_SHOULD_SKIP_THIS

template <class... Types>
Variant<std::tuple<Types...>>
Variant<std::tuple<Types...>>::create(const std::tuple<Types...>& data)
{
  // create a vector containing all tuple values as variants
  std::vector<Glib::VariantBase> variants;
  detail::expand_tuple(variants, data, detail::index_sequence_for<Types...>{});

  using var_ptr = GVariant*;
  std::unique_ptr<var_ptr[]> var_array(new var_ptr[sizeof... (Types)]);

  for (std::vector<VariantBase>::size_type i = 0; i < variants.size(); i++)
    var_array[i] = const_cast<GVariant*>(variants[i].gobj());

  Variant<std::tuple<Types...>> result = Variant<std::tuple<Types...>>(
          g_variant_new_tuple(var_array.get(), variants.size()));

  return result;
}

template <class... Types>
template <class T>
T Variant<std::tuple<Types...>>::get_child(gsize index) const
{
  Variant<T> entry;
  VariantContainerBase::get_child(entry, index);
  return entry.get();
}

template <class... Types>
template <class T>
Variant<T> Variant<std::tuple<Types...>>::get_child_variant(gsize index) const
{
  Variant<T> entry;
  VariantContainerBase::get_child(entry, index);
  return entry;
}

#ifndef DOXYGEN_SHOULD_SKIP_THIS
namespace detail
{
// swallows any argument
template <class T>
constexpr int any_arg(T&& /* arg */)
{
  return 0;
}

template <class Tuple, std::size_t... Is>
void assign_tuple(std::vector<VariantBase> &variants, Tuple & t, detail::index_sequence<Is...>)
{
  int i = 0;
  using swallow = int[]; // ensures left to right order
  (void)swallow {(any_arg(std::get<Is>(t) = VariantBase::cast_dynamic<Variant<typename std::tuple_element<Is, Tuple>::type > >(variants[i++]).get()))...};
}
} // namespace detail
#endif // DOXYGEN_SHOULD_SKIP_THIS

template <class... Types>
std::tuple<Types...> Variant<std::tuple<Types...>>::get() const
{
  std::tuple<Types...> data;
  int i = 0;

  std::vector<VariantBase> variants;
  using swallow = int[]; // ensures left to right order
  auto expander = [&variants, &i](const VariantBase &variant) -> int
  {
    variants.push_back(variant);
    return i++;
  };
  (void)swallow{(expander(get_child_variant<Types>(i)))...};
  detail::assign_tuple(variants, data, detail::index_sequence_for<Types...>{});

  return data;
}

template< class... Types>
VariantIter Variant<std::tuple<Types...>>::get_iter() const
{
  const auto type = variant_type();
  return VariantContainerBase::get_iter(type);
}

#ifndef DOXYGEN_SHOULD_SKIP_THIS
// This is needed so Glib::VariantBase can be used with
// Glib::Value and _WRAP_PROPERTY in Gio::Action and elsewhere.
template <>
class GLIBMM_API Value<Glib::VariantBase> : public ValueBase_Variant
{
public:
  using CppType = Glib::VariantBase;

  void set(CppType data);
  CppType get() const;
};
#endif /* DOXYGEN_SHOULD_SKIP_THIS */

} // namespace Glib