regina::PacketData< Held > Class Template Reference

A lightweight helper class that allows an object of type Held to connect with the wrapped packet class that contains it. More...

#include <packet/packet.h>

Classes
class	ChangeEventSpan
	An object that facilitates firing packetToBeChanged() and packetWasChanged() events. More...

Public Member Functions
	PacketData ()=default
	Default constructor that sets heldBy_ to HELD_BY_NONE. More...
	PacketData (const PacketData &) noexcept
	Copy constructor that ignores its argument, and instead sets heldBy_ to HELD_BY_NONE. More...
PacketData &	operator= (const PacketData &)
	Assignment operator that ignores its argument and does nothing. More...
std::shared_ptr< PacketOf< Held > >	packet ()
	Returns the packet that holds this data, if there is one. More...
std::shared_ptr< const PacketOf< Held > >	packet () const
	Returns the packet that holds this data, if there is one. More...
std::string	anonID () const
	A unique string ID that can be used in place of a packet ID. More...

Protected Attributes
PacketHeldBy	heldBy_ { HELD_BY_NONE }
	Indicates whether this Held object is in fact the inherited data for a PacketOf<Held>. More...

Friends
class	PacketOf< Held >

Detailed Description

template<typename Held>
class regina::PacketData< Held >

A lightweight helper class that allows an object of type Held to connect with the wrapped packet class that contains it.

For every wrapped packet type of the form PacketOf<Held>, the corresponding class Held must derive from PacketData<Held>. See the Packet class notes for more information about packets, and for what else must be implemented for each wrapped packet type.

This base class is extremely lightweight: the only data that it contains is a single PacketHeldBy enumeration value. All of the class constructors set this value to HELD_BY_NONE; it is the responsibility of subclasses (e.g., PacketOf<Held>) to change this where necessary.

Constructor & Destructor Documentation

PacketData() [1/2]

template<typename Held >

regina::PacketData< Held >::PacketData ( )

default

Default constructor that sets heldBy_ to HELD_BY_NONE.

PacketData() [2/2]

template<typename Held >

regina::PacketData< Held >::PacketData ( const PacketData< Held > &  )

inlinenoexcept

Copy constructor that ignores its argument, and instead sets heldBy_ to HELD_BY_NONE.

This is because heldBy_ stores information about the C++ type of this object, not the object being copied.

This constructor is provided so that Held can (if it wants) use an implicitly-declared copy or move constructor.

Member Function Documentation

anonID()

template<typename Held >

std::string regina::PacketData< Held >::anonID

A unique string ID that can be used in place of a packet ID.

This is an alternative to Packet::internalID(), and is designed for use when Held is not actually wrapped by a PacketOf<Held>. (An example of such a scenario is when a normal surface list needs to write its triangulation to file, but the triangulation is a standalone object that is not stored in a packet.)

The ID that is returned will:

• remain fixed throughout the lifetime of the program for a given object, even if the contents of the object are changed;
• not clash with the anonID() returned from any other object, or with the internalID() returned from any packet of any type;

These IDs are not preserved when copying or moving one object to another, and are not preserved when writing to a Regina data file and then reloading the file contents.

Warning

If this object is wrapped in a PacketOf<Held>, then anonID() and Packet::internalID() may return different values.

See Packet::internalID() for further details.

Returns

a unique ID that identifies this object.

operator=()

template<typename Held >

PacketData & regina::PacketData< Held >::operator= ( const PacketData< Held > &  )

inline

Assignment operator that ignores its argument and does nothing.

This is because heldBy_ stores information about the C++ type of this object, not the object being copied.

This operator is provided so that Held can (if it wants) use an implicitly-declared copy or move assignment operator.

Returns

a reference to this object.

packet() [1/2]

template<typename Held >

std::shared_ptr< PacketOf< Held > > regina::PacketData< Held >::packet ( )

inline

Returns the packet that holds this data, if there is one.

If this object is being held by a packet p of type PacketOf<Held>, then that packet p will be returned. Otherwise, if this is a "standalone" object of type Held, then this routine will return null.

There is a special case when dealing with a packet q that holds a SnapPea triangulation. Here q is of type PacketOf<SnapPeaTriangulation>, and it holds a Triangulation<3> "indirectly" in the sense that Packetof<SnapPeaTriangulation> derives from SnapPeaTriangulation, which in turn derives from Triangulation<3>. In this scenario:

• calling Triangulation<3>::packet() will return null, since there is no "direct" PacketOf<Triangulation<3>>;
• calling SnapPeaTriangulation::packet() will return the enclosing packet q, since there is a PacketOf<SnapPeaTriangulation>;
• calling the special routine Triangulation<3>::inAnyPacket() will also return the "indirect" enclosing packet q.

The function inAnyPacket() is specific to Triangulation<3>, and is not offered for other Held types.

Returns

the packet that holds this data, or null if this data is not (directly) held by a packet.

packet() [2/2]

template<typename Held >

std::shared_ptr< const PacketOf< Held > > regina::PacketData< Held >::packet ( ) const

inline

Returns the packet that holds this data, if there is one.

See the non-const version of this function for further details, and in particular for how this functions operations in the special case of a packet that holds a SnapPea triangulation.

Returns

the packet that holds this data, or null if this data is not (directly) held by a packet.

Member Data Documentation

heldBy_

template<typename Held >

PacketHeldBy regina::PacketData< Held >::heldBy_ { HELD_BY_NONE }

protected

Indicates whether this Held object is in fact the inherited data for a PacketOf<Held>.

As a special case, this field is also used to indicate when a Triangulation<3> is in fact the inherited data for a SnapPeaTriangulation. See the PacketHeldBy enumeration for more details on the different values that this data member can take.

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The documentation for this class was generated from the following file:

• packet/packet.h