glibmm 2.78.0
Public Member Functions | Static Public Member Functions | Protected Attributes | Related Functions | List of all members
Glib::VariantType Class Reference

VariantType - The VariantBase type system. More...

#include <glibmm/varianttype.h>

Public Member Functions

 VariantType ()
 Constructs an invalid object. More...
 
 VariantType (GVariantType * castitem, bool make_a_copy=false)
 
 VariantType (const VariantType & src)
 
VariantTypeoperator= (const VariantType & src)
 
 VariantType (VariantType && other) noexcept
 
VariantTypeoperator= (VariantType && other) noexcept
 
 ~VariantType () noexcept
 
void swap (VariantType & other) noexcept
 
GVariantType * gobj ()
 
const GVariantType * gobj () const
 
GVariantType * gobj_copy () const
 Provides access to the underlying C instance. The caller is responsible for freeing it. Use when directly setting fields in structs. More...
 
 VariantType (const GVariantType * castitem)
 Copy the C item into a new VariantType instance. More...
 
 VariantType (const std::string & type_string)
 Creates a new VariantType corresponding to the type string given by type_string. More...
 
VariantTypeoperator= (const GVariantType * castitem)
 
gsize get_string_length () const
 Returns the length of the type string corresponding to the given type. More...
 
std::string get_string () const
 Returns the type string corresponding to the given type. More...
 
bool is_definite () const
 Determines if the given type is definite (ie: not indefinite). More...
 
bool is_container () const
 Determines if the given type is a container type. More...
 
bool is_basic () const
 Determines if the given type is a basic type. More...
 
bool is_maybe () const
 Determines if the given type is a maybe type. More...
 
bool is_array () const
 Determines if the given type is an array type. More...
 
bool is_tuple () const
 Determines if the given type is a tuple type. More...
 
bool is_dict_entry () const
 Determines if the given type is a dictionary entry type. More...
 
bool is_variant () const
 Determines if the given type is the variant type. More...
 
guint hash () const
 Hashes type. More...
 
bool equal (const VariantType & other) const
 Compares *this and other for equality. More...
 
bool is_subtype_of (const VariantType & supertype) const
 Checks if type is a subtype of supertype. More...
 
VariantType element () const
 Determines the element type of an array or maybe type. More...
 
gsize n_items () const
 Determines the number of items contained in a tuple or dictionary entry type. More...
 
VariantType key () const
 Determines the key type of a dictionary entry type. More...
 
VariantType value () const
 Determines the value type of a dictionary entry type. More...
 
std::vector< VariantTypeget_item_types () const
 Determines the item types of a tuple or dictionary entry type. More...
 

Static Public Member Functions

static VariantType create_array (const VariantType &element)
 Constructs the type corresponding to an array of elements of the type type. More...
 
static VariantType create_maybe (const VariantType &element)
 Constructs the type corresponding to a maybe instance containing type type or Nothing. More...
 
static VariantType create_tuple (const std::vector< VariantType > & items)
 Constructs a new tuple type, from items. More...
 
static VariantType create_dict_entry (const VariantType &key, const VariantType &value)
 Constructs the type corresponding to a dictionary entry with a key of type key and a value of type value. More...
 

Protected Attributes

GVariantType * gobject_
 

Related Functions

(Note that these are not member functions.)

void swap (VariantType & lhs, VariantType & rhs) noexcept
 
Glib::VariantType wrap (GVariantType * object, bool take_copy=false)
 A Glib::wrap() method for this object. More...
 

Detailed Description

VariantType - The VariantBase type system.

The VariantBase type system is based, in large part, on the D-Bus type system, with two major changes and some minor lifting of restrictions. The D-Bus specification, therefore, provides a significant amount of information that is useful when working with VariantBase.

The first major change with respect to the D-Bus type system is the introduction of maybe (or "nullable") types. Any type in VariantBase can be converted to a maybe type, in which case, "nothing" (or "null") becomes a valid value. Maybe types have been added by introducing the character "m" to type strings.

The second major change is that the VariantBase type system supports the concept of "indefinite types" – types that are less specific than the normal types found in D-Bus. For example, it is possible to speak of "an array of any type" in VariantBase, where the D-Bus type system would require you to speak of "an array of integers" or "an array of strings". Indefinite types have been added by introducing the characters "*", "?" and "r" to type strings.

Finally, all arbitrary restrictions relating to the complexity of types are lifted along with the restriction that dictionary entries may only appear nested inside of arrays.

Just as in D-Bus, VariantBase types are described with strings ("type strings"). Subject to the differences mentioned above, these strings are of the same form as those found in D-Bus. Note, however: D-Bus always works in terms of messages and therefore individual type strings appear nowhere in its interface. Instead, "signatures" are a concatenation of the strings of the type of each argument in a message. VariantBase deals with single values directly so VariantBase type strings always describe the type of exactly one value. This means that a D-Bus signature string is generally not a valid VariantBase type string – except in the case that it is the signature of a message containing exactly one argument.

An indefinite type is similar in spirit to what may be called an abstract type in other type systems. No value can exist that has an indefinite type as its type, but values can exist that have types that are subtypes of indefinite types. That is to say, VariantBase::get_type() will never return an indefinite type, but calling VariantBase::is_of_type() with an indefinite type may return true. For example, you cannot have a value that represents "an array of no particular type", but you can have an "array of integers" which certainly matches the type of "an array of no particular type", since "array of integers" is a subtype of "array of no particular type".

This is similar to how instances of abstract classes may not directly exist in other type systems, but instances of their non-abstract subtypes may. For example, in gtkmm, no object that has the type of Gtk::Widget can exist (since Gtk::Widget is an abstract class), but a Gtk::Window can certainly be instantiated, and you would say that the Gtk::Window is a Gtk::Widget (since Gtk::Window is a subclass of Gtk::Widget).

See the underlying GVariantType documentation for a detailed description of the VariantBase type strings.

Since glibmm 2.28:

Constructor & Destructor Documentation

◆ VariantType() [1/6]

Glib::VariantType::VariantType ( )

Constructs an invalid object.

E.g. for output arguments to methods. There is not much you can do with the object before it has been assigned a valid value.

◆ VariantType() [2/6]

Glib::VariantType::VariantType ( GVariantType *  castitem,
bool  make_a_copy = false 
)
explicit

◆ VariantType() [3/6]

Glib::VariantType::VariantType ( const VariantType src)

◆ VariantType() [4/6]

Glib::VariantType::VariantType ( VariantType &&  other)
noexcept

◆ ~VariantType()

Glib::VariantType::~VariantType ( )
noexcept

◆ VariantType() [5/6]

Glib::VariantType::VariantType ( const GVariantType *  castitem)
explicit

Copy the C item into a new VariantType instance.

◆ VariantType() [6/6]

Glib::VariantType::VariantType ( const std::string type_string)
explicit

Creates a new VariantType corresponding to the type string given by type_string.

It is a programmer error to call this function with an invalid type string. Use string_is_valid() if you are unsure.

Member Function Documentation

◆ create_array()

static VariantType Glib::VariantType::create_array ( const VariantType element)
static

Constructs the type corresponding to an array of elements of the type type.

It is appropriate to call g_variant_type_free() on the return value.

Since glibmm 2.24:
Parameters
elementA VariantType.
Returns
A new array VariantType.

◆ create_dict_entry()

static VariantType Glib::VariantType::create_dict_entry ( const VariantType key,
const VariantType value 
)
static

Constructs the type corresponding to a dictionary entry with a key of type key and a value of type value.

It is appropriate to call g_variant_type_free() on the return value.

Since glibmm 2.24:
Parameters
keyA basic VariantType.
valueA VariantType.
Returns
A new dictionary entry VariantType.

◆ create_maybe()

static VariantType Glib::VariantType::create_maybe ( const VariantType element)
static

Constructs the type corresponding to a maybe instance containing type type or Nothing.

It is appropriate to call g_variant_type_free() on the return value.

Since glibmm 2.24:
Parameters
elementA VariantType.
Returns
A new maybe VariantType.

◆ create_tuple()

static VariantType Glib::VariantType::create_tuple ( const std::vector< VariantType > &  items)
static

Constructs a new tuple type, from items.

Parameters
itemsA vector of VariantTypes, one for each item.
Returns
A new tuple VariantType.
Since glibmm 2.36:

◆ element()

VariantType Glib::VariantType::element ( ) const

Determines the element type of an array or maybe type.

This function may only be used with array or maybe types.

Since glibmm 2.24:
Returns
The element type of type.

◆ equal()

bool Glib::VariantType::equal ( const VariantType other) const

Compares *this and other for equality.

Only returns true if the types are exactly equal. Even if one type is an indefinite type and the other is a subtype of it, false will be returned if they are not exactly equal. If you want to check for subtypes, use is_subtype_of().

Parameters
otherThe VariantType to compare with.
Returns
true if *this and other are exactly equal.
Since glibmm 2.24:

◆ get_item_types()

std::vector< VariantType > Glib::VariantType::get_item_types ( ) const

Determines the item types of a tuple or dictionary entry type.

This function may only be used with tuple or dictionary entry types, but must not be used with the generic tuple type VARIANT_TYPE_TUPLE.

In the case of a dictionary entry type, returns a vector with 2 elements, the type of the key followed by the value type.

An empty vector is returned in case of this VariantType being VARIANT_TYPE_UNIT.

Since glibmm 2.52:
Returns
The item types of this VariantType, or an empty vector.

◆ get_string()

std::string Glib::VariantType::get_string ( ) const

Returns the type string corresponding to the given type.

The result is not nul-terminated; in order to determine its length you must call g_variant_type_get_string_length().

To get a nul-terminated string, see g_variant_type_dup_string().

Since glibmm 2.24:
Returns
The corresponding type string (not nul-terminated).

◆ get_string_length()

gsize Glib::VariantType::get_string_length ( ) const

Returns the length of the type string corresponding to the given type.

This function must be used to determine the valid extent of the memory region returned by g_variant_type_peek_string().

Since glibmm 2.24:
Returns
The length of the corresponding type string.

◆ gobj() [1/2]

GVariantType * Glib::VariantType::gobj ( )
inline

◆ gobj() [2/2]

const GVariantType * Glib::VariantType::gobj ( ) const
inline

◆ gobj_copy()

GVariantType * Glib::VariantType::gobj_copy ( ) const

Provides access to the underlying C instance. The caller is responsible for freeing it. Use when directly setting fields in structs.

◆ hash()

guint Glib::VariantType::hash ( ) const

Hashes type.

The argument type of type is only #gconstpointer to allow use with HashTable without function pointer casting. A valid VariantType must be provided.

Since glibmm 2.24:
Returns
The hash value.

◆ is_array()

bool Glib::VariantType::is_array ( ) const

Determines if the given type is an array type.

This is true if the type string for type starts with an 'a'.

This function returns true for any indefinite type for which every definite subtype is an array type – G_VARIANT_TYPE_ARRAY, for example.

Since glibmm 2.24:
Returns
true if type is an array type.

◆ is_basic()

bool Glib::VariantType::is_basic ( ) const

Determines if the given type is a basic type.

Basic types are booleans, bytes, integers, doubles, strings, object paths and signatures.

Only a basic type may be used as the key of a dictionary entry.

This function returns false for all indefinite types except G_VARIANT_TYPE_BASIC.

Since glibmm 2.24:
Returns
true if type is a basic type.

◆ is_container()

bool Glib::VariantType::is_container ( ) const

Determines if the given type is a container type.

Container types are any array, maybe, tuple, or dictionary entry types plus the variant type.

This function returns true for any indefinite type for which every definite subtype is a container – G_VARIANT_TYPE_ARRAY, for example.

Since glibmm 2.24:
Returns
true if type is a container type.

◆ is_definite()

bool Glib::VariantType::is_definite ( ) const

Determines if the given type is definite (ie: not indefinite).

A type is definite if its type string does not contain any indefinite type characters ('*', '?', or 'r').

A Variant instance may not have an indefinite type, so calling this function on the result of g_variant_get_type() will always result in true being returned. Calling this function on an indefinite type like G_VARIANT_TYPE_ARRAY, however, will result in false being returned.

Since glibmm 2.24:
Returns
true if type is definite.

◆ is_dict_entry()

bool Glib::VariantType::is_dict_entry ( ) const

Determines if the given type is a dictionary entry type.

This is true if the type string for type starts with a '{'.

This function returns true for any indefinite type for which every definite subtype is a dictionary entry type – G_VARIANT_TYPE_DICT_ENTRY, for example.

Since glibmm 2.24:
Returns
true if type is a dictionary entry type.

◆ is_maybe()

bool Glib::VariantType::is_maybe ( ) const

Determines if the given type is a maybe type.

This is true if the type string for type starts with an 'm'.

This function returns true for any indefinite type for which every definite subtype is a maybe type – G_VARIANT_TYPE_MAYBE, for example.

Since glibmm 2.24:
Returns
true if type is a maybe type.

◆ is_subtype_of()

bool Glib::VariantType::is_subtype_of ( const VariantType supertype) const

Checks if type is a subtype of supertype.

This function returns true if type is a subtype of supertype. All types are considered to be subtypes of themselves. Aside from that, only indefinite types can have subtypes.

Since glibmm 2.24:
Parameters
supertypeA VariantType.
Returns
true if type is a subtype of supertype.

◆ is_tuple()

bool Glib::VariantType::is_tuple ( ) const

Determines if the given type is a tuple type.

This is true if the type string for type starts with a '(' or if type is G_VARIANT_TYPE_TUPLE.

This function returns true for any indefinite type for which every definite subtype is a tuple type – G_VARIANT_TYPE_TUPLE, for example.

Since glibmm 2.24:
Returns
true if type is a tuple type.

◆ is_variant()

bool Glib::VariantType::is_variant ( ) const

Determines if the given type is the variant type.

Since glibmm 2.24:
Returns
true if type is the variant type.

◆ key()

VariantType Glib::VariantType::key ( ) const

Determines the key type of a dictionary entry type.

This function may only be used with a dictionary entry type. Other than the additional restriction, this call is equivalent to g_variant_type_first().

Since glibmm 2.24:
Returns
The key type of the dictionary entry.

◆ n_items()

gsize Glib::VariantType::n_items ( ) const

Determines the number of items contained in a tuple or dictionary entry type.

This function may only be used with tuple or dictionary entry types, but must not be used with the generic tuple type G_VARIANT_TYPE_TUPLE.

In the case of a dictionary entry type, this function will always return 2.

Since glibmm 2.24:
Returns
The number of items in type.

◆ operator=() [1/3]

VariantType & Glib::VariantType::operator= ( const GVariantType *  castitem)

◆ operator=() [2/3]

VariantType & Glib::VariantType::operator= ( const VariantType src)

◆ operator=() [3/3]

VariantType & Glib::VariantType::operator= ( VariantType &&  other)
noexcept

◆ swap()

void Glib::VariantType::swap ( VariantType other)
noexcept

◆ value()

VariantType Glib::VariantType::value ( ) const

Determines the value type of a dictionary entry type.

This function may only be used with a dictionary entry type.

Since glibmm 2.24:
Returns
The value type of the dictionary entry.

Friends And Related Function Documentation

◆ swap()

void swap ( VariantType lhs,
VariantType rhs 
)
related
Parameters
lhsThe left-hand side
rhsThe right-hand side

◆ wrap()

Glib::VariantType wrap ( GVariantType *  object,
bool  take_copy = false 
)
related

A Glib::wrap() method for this object.

Parameters
objectThe C instance.
take_copyFalse if the result should take ownership of the C instance. True if it should take a new copy or ref.
Returns
A C++ instance that wraps this C instance.

Member Data Documentation

◆ gobject_

GVariantType* Glib::VariantType::gobject_
protected