VariantType

A type in the glib.variant.VariantG type system.

This section introduces the glib.variant.VariantG type system. It 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 glib.variant.VariantG.

The first major change with respect to the D-Bus type system is the introduction of maybe (or ‘nullable’) types. Any type in glib.variant.VariantG 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 glib.variant.VariantG 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 glib.variant.VariantG, 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, glib.variant.VariantG 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. glib.variant.VariantG deals with single values directly so glib.variant.VariantG type strings always describe the type of exactly one value. This means that a D-Bus signature string is generally not a valid glib.variant.VariantG 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, glib.variant.VariantG.getType will never return an indefinite type, but calling glib.variant.VariantG.isOfType 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 GTK, no object that has the type of [gtk.widget.Widget] can exist (since gtk.widget.Widget is an abstract class), but a [gtk.window.Window] can certainly be instantiated, and you would say that a gtk.window.Window is a gtk.widget.Widget (since gtk.window.Window is a subclass of gtk.widget.Widget).

Two types may not be compared by value; use glib.variant_type.VariantType.equal or glib.variant_type.VariantType.isSubtypeOf May be copied using glib.variant_type.VariantType.copy and freed using glib.variant_type.VariantType.free.

GVariant Type Strings

A glib.variant.VariantG type string can be any of the following:

  • any basic type string (listed below)
  • v, r or *
  • one of the characters a or m, followed by another type string
  • the character (, followed by a concatenation of zero or more other type strings, followed by the character )
  • the character {, followed by a basic type string (see below), followed by another type string, followed by the character }

A basic type string describes a basic type (as per glib.variant_type.VariantType.isBasic) and is always a single character in length. The valid basic type strings are b, y, n, q, i, u, x, t, h, d, s, o, g and ?.

The above definition is recursive to arbitrary depth. aaaaai and (ui(nq((y)))s) are both valid type strings, as is a(aa(ui)(qna{ya(yd)})). In order to not hit memory limits, glib.variant.VariantG imposes a limit on recursion depth of 65 nested containers. This is the limit in the D-Bus specification (64) plus one to allow a [gio.dbus_message.DBusMessage] to be nested in a top-level tuple.

The meaning of each of the characters is as follows:

  • b: the type string of G_VARIANT_TYPE_BOOLEAN; a boolean value.
  • y: the type string of G_VARIANT_TYPE_BYTE; a byte.
  • n: the type string of G_VARIANT_TYPE_INT16; a signed 16 bit integer.
  • q: the type string of G_VARIANT_TYPE_UINT16; an unsigned 16 bit integer.
  • i: the type string of G_VARIANT_TYPE_INT32; a signed 32 bit integer.
  • u: the type string of G_VARIANT_TYPE_UINT32; an unsigned 32 bit integer.
  • x: the type string of G_VARIANT_TYPE_INT64; a signed 64 bit integer.
  • t: the type string of G_VARIANT_TYPE_UINT64; an unsigned 64 bit integer.
  • h: the type string of G_VARIANT_TYPE_HANDLE; a signed 32 bit value that, by convention, is used as an index into an array of file descriptors that are sent alongside a D-Bus message.
  • d: the type string of G_VARIANT_TYPE_DOUBLE; a double precision floating point value.
  • s: the type string of G_VARIANT_TYPE_STRING; a string.
  • o: the type string of G_VARIANT_TYPE_OBJECT_PATH; a string in the form of a D-Bus object path.
  • g: the type string of G_VARIANT_TYPE_SIGNATURE; a string in the form of a D-Bus type signature.
  • ?: the type string of G_VARIANT_TYPE_BASIC; an indefinite type that is a supertype of any of the basic types.
  • v: the type string of G_VARIANT_TYPE_VARIANT; a container type that contain any other type of value.
  • a: used as a prefix on another type string to mean an array of that type; the type string ai, for example, is the type of an array of signed 32-bit integers.
  • m: used as a prefix on another type string to mean a ‘maybe’, or ‘nullable’, version of that type; the type string ms, for example, is the type of a value that maybe contains a string, or maybe contains nothing.
  • (): used to enclose zero or more other concatenated type strings to create a tuple type; the type string (is), for example, is the type of a pair of an integer and a string.
  • r: the type string of G_VARIANT_TYPE_TUPLE; an indefinite type that is a supertype of any tuple type, regardless of the number of items.
  • {}: used to enclose a basic type string concatenated with another type string to create a dictionary entry type, which usually appears inside of an array to form a dictionary; the type string a{sd}, for example, is the type of a dictionary that maps strings to double precision floating point values.

    The first type (the basic type) is the key type and the second type is the value type. The reason that the first type is restricted to being a basic type is so that it can easily be hashed.

  • *: the type string of G_VARIANT_TYPE_ANY; the indefinite type that is a supertype of all types. Note that, as with all type strings, this character represents exactly one type. It cannot be used inside of tuples to mean ‘any number of items’.

Any type string of a container that contains an indefinite type is, itself, an indefinite type. For example, the type string a* (corresponding to G_VARIANT_TYPE_ARRAY) is an indefinite type that is a supertype of every array type. (*s) is a supertype of all tuples that contain exactly two items where the second item is a string.

a{?*} is an indefinite type that is a supertype of all arrays containing dictionary entries where the key is any basic type and the value is any type at all. This is, by definition, a dictionary, so this type string corresponds to G_VARIANT_TYPE_DICTIONARY. Note that, due to the restriction that the key of a dictionary entry must be a basic type, {**} is not a valid type string.

Constructors

this
this(string typeString)

Creates a new #GVariantType corresponding to the type string given by type_string. It is appropriate to call glib.variant_type.VariantType.free on the return value.

Members

Functions

copy
glib.variant_type.VariantType copy()

Makes a copy of a #GVariantType. It is appropriate to call glib.variant_type.VariantType.free on the return value. type may not be null.

dupString
string dupString()

Returns a newly-allocated copy of the type string corresponding to type. The returned string is nul-terminated. It is appropriate to call glib.global.gfree on the return value.

element
glib.variant_type.VariantType element()

Determines the element type of an array or maybe type.

equal
bool equal(glib.variant_type.VariantType type2)

Compares type1 and type2 for equality.

first
glib.variant_type.VariantType first()

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

getStringLength
size_t getStringLength()

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 glib.variant_type.VariantType.peekString.

hash
uint hash()

Hashes type.

isArray
bool isArray()

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

isBasic
bool isBasic()

Determines if the given type is a basic type.

isContainer
bool isContainer()

Determines if the given type is a container type.

isDefinite
bool isDefinite()

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

isDictEntry
bool isDictEntry()

Determines if the given type is a dictionary entry type. This is true if the type string for type starts with a '{'.

isMaybe
bool isMaybe()

Determines if the given type is a maybe type. This is true if the type string for type starts with an 'm'.

isSubtypeOf
bool isSubtypeOf(glib.variant_type.VariantType supertype)

Checks if type is a subtype of supertype.

isTuple
bool isTuple()

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.

isVariant
bool isVariant()

Determines if the given type is the variant type.

key
glib.variant_type.VariantType key()

Determines the key type of a dictionary entry type.

nItems
size_t nItems()

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

next
glib.variant_type.VariantType next()

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

value
glib.variant_type.VariantType value()

Determines the value type of a dictionary entry type.

Static functions

checked
glib.variant_type.VariantType checked(string typeString)
create
VariantType create()

Template for creating a new VariantType from one or more D types

getStr
string getStr()

Template to get a variant type string from one or more D types (type strings are concatenated)

newArray
glib.variant_type.VariantType newArray(glib.variant_type.VariantType element)

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

newDictEntry
glib.variant_type.VariantType newDictEntry(glib.variant_type.VariantType key, glib.variant_type.VariantType value)

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

newMaybe
glib.variant_type.VariantType newMaybe(glib.variant_type.VariantType element)

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

newTuple
glib.variant_type.VariantType newTuple(glib.variant_type.VariantType[] items)

Constructs a new tuple type, from items.

stringGetDepth
size_t stringGetDepth(string typeString)
stringIsValid
bool stringIsValid(string typeString)

Checks if type_string is a valid GVariant type string. This call is equivalent to calling glib.variant_type.VariantType.stringScan and confirming that the following character is a nul terminator.

stringScan
bool stringScan(string string_, string limit, string endptr)

Scan for a single complete and valid GVariant type string in string. The memory pointed to by limit (or bytes beyond it) is never accessed.

Inherited Members

From Boxed

cInstancePtr
void* cInstancePtr;

Pointer to the C boxed value

getType
GType getType()

Get the GType of this boxed type.

gType
GType gType [@property getter]

Boxed GType property.

self
Boxed self()

Convenience method to return this cast to a type. For use in D with statements.

copy_
void* copy_()

Make a copy of the wrapped C boxed data.

boxedCopy
void* boxedCopy(void* cBoxed)

Copy a C boxed value using g_boxed_copy.

boxedFree
void boxedFree(void* cBoxed)

Free a C boxed value using g_boxed_free.