Variant Class Reference

Inherits from	`BasicType`
Declared in	`flip/Variant.h`

template <class T> class Variant;

flip::Variant is a one element constrained container.

The Variant itself provides support for modification introspection. When modifying the content of the Variant, the previous representation of the variant is still present.

Internally the Variant is just a Collection with a constraint on size.

Important: A variant must be filled with exactly an element before commit is called. As a result, a Variant cannot be a member of the root class of a document.

Template Parameters

`T`	The type of the elements. `T` must inherit from `flip::Object`

Member Types

`value_type`	`T`
`reference`	`T &`
`const_reference`	`const T &`
`pointer`	`T *`
`const_pointer`	`const T *`

Member Functions Synopsys

Constructor	Constructs the `Variant`
Destructor	Destructs the `Variant`
`operator =`	Assigns values to the container

Document Management

`document`	Returns the document to which the object is attached to
`ref`	Returns the unique reference number of the object
`added`	Returns `true` iff the object was just attached to the document tree
`removed`	Returns `true` iff the object was just detached from the document tree
`resident`	Returns `true` iff the object was neither attached nor detached from the document tree
`changed`	Returns `true` iff the object or one of its children was modified
`ancestor`	Returns a reference to a parent in the current parent chain of the object
`disable_in_undo`	Disables the record state modification in history
`inherit_in_undo`	Inherits the record state modification in history
`is_in_undo_enabled`	Returns `true` iff this object modifications are recorded in history
`revert`	Reverts all the changes made to the object and its children if any
`assign`	Replaces the content of the object with the content of the provided object

Element Access

`operator T &`	Access element
`use`	Access element
`before`	Access previous version of element

Modifiers

reset

Resets element in-place

Member Functions

Constructor

Variant ();                       (1)
Variant (const Variant & other);  (2)

Default constructor, constructs an empty variant.
Copy constructor. Constructs the container with copy of elements of other.

Destructor

~Variant ();

Destructor.

`operator =`

Variant & operator = (const Variant & other);
template <class U>
Variant & operator = (const U & other);

Copy assignment operator.

`document`

DocumentBase & document () const;

Returns the document to which the object is attached to.

WARNING: Temporary flip objects are not attached to a document

`ref`

const Ref & ref () const;

Returns the unique reference number of the object.

`added`

bool  added () const;

Returns true iff the object was just attached to the document tree.

Example :

void  Observer::document_changed (Note & note)
{
   if (note.added ())
   {
      // A note was added to the document. Create the corresponding
      // view element
      note.entity ().emplace <NoteView> ();
   }
   [...]
}

`removed`

bool  removed () const;

Returns true iff the object was just detached from the document tree.

Example :

void  Observer::document_changed (Note & note)
{
   [...]
   if (note.removed ())
   {
      // A note was removed from the document. Release the corresponding
      // view element
      note.entity ().erase <NoteView> ();
   }
}

`resident`

bool  resident () const;

Returns true iff the object was neither attached nor detached from the document tree.

An object can be resident but moved. In this case the iterator pointing to it will allow to detect the move.

Example :

void  Observer::document_changed (Array <Track> & tracks)
{
   auto it = tracks.begin ();
   auto it_end = tracks.end ();
   for (; it != it_end ; ++it)
   {
      Track & track = *it;
      if (it.added () && track.resident ())
      {
         // the track was moved in the container
         // this is the destination position
      }
      if (it.added () && track.resident ())
      {
         // the track was moved in the container
         // this is the source position
      }
   }
}

`changed`

bool  changed () const;

Returns true iff the object or one of its children was modified.

Example :

void  Observer::document_changed (Note & note)
{
   auto & view = note.entity ().use <ViewNote> ();
   if (note.changed ())
   {
      // one or more properties of the note changed
      if (note.position.changed ())
      {
         view.set_position (note.position);
      }
      if (note.duration.changed ())
      {
         view.set_duration (note.duration);
      }
   }
}

`ancestor`

template <class T>   T &   ancestor ();
template <class T>   const T &   ancestor () const;

Returns a reference to a parent in the current parent chain of the object.

Note: If an object or its parent is moved from one container to another, this function will always return the current parent, that is not the previous one

`disable_in_undo`

void   disable_in_undo ();

Disables the record state modification in history of the object and its subtree if any.

Example :

void  add_user (Root & root)
{
   // emplace a new User of the document to store
   // user specific data. User is constructed with
   // the unique user id number given at document
   // creation
   User & user = root.users.emplace <User> (root.document ().user ());
   // we don't want the scroll position in the document
   // to be part of undo
   user.scroll_position.disable_in_undo ();
}

`inherit_in_undo`

void   inherit_in_undo ();

Inherits the record state modification in history of the object and its subtree if any, from its parent state. This is the default mode.

Note: If the Root object of the tree is in inherited mode, then it is considered as enabled in undo.

`is_in_undo_enabled`

bool  is_in_undo_enabled () const;

Returns true iff this object modifications are recorded in history. The function recursively search for disabled state starting from the object itself and navigating through the parent objects, if the state is inherited.

`revert`

void  revert () const;

Reverts all the changes make to the object and its children if any.

Example :

// initially, note.position == 1
note.position = 2;
note.revert ();
// now, note.position == 1

`assign`

void  assign (const Type & rhs);

Replaces the content of the object with the content of the provided object. Both objects need to be bound to a document for the function to succeed.

Example :

// initially :
// note.position == 1
// note.duration == 3
// note2.position == 2
// note2.duration == 1
note.assign (note2);
// now :
// note.position == 2
// note.duration == 1

`operator T &`

operator T & () const;

Returns a reference to the element.

`use`

template <class U>
U &      use () const;

Returns a reference to the element as type U.

`before`

T &   before () const;
template <class U>
U &      before () const;

Returns a reference to previous version of the element.

`reset`

template <class... Args>
T &      reset (Args &&... args);     (1)
template <class U, class... Args>
U &      reset (Args &&... args);     (2)
T &      reset (const Mold & mold);   (3)
template <class U>
U &      reset (const Mold & mold);   (4)

Resets to a new element constructed in-place with arguments args.
Resets to a new element of type U constructed in-place with arguments args.
Resets to a new element casted from mold.
Resets to a new element of type U casted from mold.

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