GI.GLib.Structs.VariantType

This section introduces the GVariant 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 GVariant.

The first major change with respect to the D-Bus type system is the introduction of maybe (or "nullable") types. Any type in GVariant 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 GVariant 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 GVariant, 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, GVariant 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. GVariant deals with single values directly so GVariant type strings always describe the type of exactly one value. This means that a D-Bus signature string is generally not a valid GVariant 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, variantGetType will never return an indefinite type, but calling variantIsOfType 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 GtkBin can exist (since GtkBin is an abstract class), but a GtkWindow can certainly be instantiated, and you would say that the GtkWindow is a GtkBin (since GtkWindow is a subclass of GtkBin).

GVariant Type Strings

A GVariant 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 variantTypeIsBasic) 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, GVariant 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 GDBusMessage 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.

Exported types

newtype VariantType

Memory-managed wrapper type.

Constructors

VariantType (ManagedPtr VariantType)

Instances

Eq VariantType

Defined in GI.GLib.Structs.VariantType

Methods

(==) :: VariantType -> VariantType -> Bool

(/=) :: VariantType -> VariantType -> Bool

GBoxed VariantType

Defined in GI.GLib.Structs.VariantType

ManagedPtrNewtype VariantType

Defined in GI.GLib.Structs.VariantType

Methods

toManagedPtr :: VariantType -> ManagedPtr VariantType

TypedObject VariantType

Defined in GI.GLib.Structs.VariantType

Methods

glibType :: IO GType

HasParentTypes VariantType

Defined in GI.GLib.Structs.VariantType

IsGValue (Maybe VariantType)

Convert VariantType to and from GValue. See toGValue and fromGValue.

Defined in GI.GLib.Structs.VariantType

Methods

gvalueGType_ :: IO GType

gvalueSet_ :: Ptr GValue -> Maybe VariantType -> IO ()

gvalueGet_ :: Ptr GValue -> IO (Maybe VariantType)

type ParentTypes VariantType

Defined in GI.GLib.Structs.VariantType

type ParentTypes VariantType = '[] :: [Type]

Methods

Click to display all available methods, including inherited ones

Methods

copy, dupString, element, equal, first, free, hash, isArray, isBasic, isContainer, isDefinite, isDictEntry, isMaybe, isSubtypeOf, isTuple, isVariant, key, nItems, next, value.

Getters

getStringLength.

Setters

None.

checked_

variantTypeChecked_ :: (HasCallStack, MonadIO m) => Text -> m VariantType

No description available in the introspection data.

copy

variantTypeCopy

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a VariantType

-> m VariantType

Returns: a new VariantType

Since 2.24

Makes a copy of a VariantType. It is appropriate to call variantTypeFree on the return value. type may not be Nothing.

dupString

variantTypeDupString

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a VariantType

-> m Text

Returns: the corresponding type string

Since 2.24

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

element

variantTypeElement

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: an array or maybe VariantType

-> m VariantType

Returns: the element type of type

Since 2.24

Determines the element type of an array or maybe type.

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

equal

variantTypeEqual

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type1: a VariantType

-> VariantType

type2: a VariantType

-> m Bool

Returns: True if type1 and type2 are exactly equal

Since 2.24

Compares type1 and type2 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 variantTypeIsSubtypeOf.

The argument types of type1 and type2 are only gconstpointer to allow use with HashTable without function pointer casting. For both arguments, a valid VariantType must be provided.

first

variantTypeFirst

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a tuple or dictionary entry VariantType

-> m VariantType

Returns: the first item type of type, or Nothing

Since 2.24

Determines the first item type 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 G_VARIANT_TYPE_TUPLE.

In the case of a dictionary entry type, this returns the type of the key.

Nothing is returned in case of type being G_VARIANT_TYPE_UNIT.

This call, together with variantTypeNext provides an iterator interface over tuple and dictionary entry types.

free

variantTypeFree

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a VariantType, or Nothing

-> m ()

Frees a VariantType that was allocated with variantTypeCopy, variantTypeNew or one of the container type constructor functions.

In the case that type is Nothing, this function does nothing.

Since 2.24

getStringLength

variantTypeGetStringLength

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a VariantType

-> m Word64

Returns: the length of the corresponding type string

Since 2.24

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().

hash

variantTypeHash

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a VariantType

-> m Word32

Returns: the hash value

Since 2.24

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.

isArray

variantTypeIsArray

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a VariantType

-> m Bool

Returns: True if type is an array type

Since 2.24

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.

isBasic

variantTypeIsBasic

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a VariantType

-> m Bool

Returns: True if type is a basic type

Since 2.24

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.

isContainer

variantTypeIsContainer

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a VariantType

-> m Bool

Returns: True if type is a container type

Since 2.24

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.

isDefinite

variantTypeIsDefinite

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a VariantType

-> m Bool

Returns: True if type is definite

Since 2.24

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 GVariant instance may not have an indefinite type, so calling this function on the result of variantGetType 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.

isDictEntry

variantTypeIsDictEntry

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a VariantType

-> m Bool

Returns: True if type is a dictionary entry type

Since 2.24

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.

isMaybe

variantTypeIsMaybe

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a VariantType

-> m Bool

Returns: True if type is a maybe type

Since 2.24

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.

isSubtypeOf

variantTypeIsSubtypeOf

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a VariantType

-> VariantType

supertype: a VariantType

-> m Bool

Returns: True if type is a subtype of supertype

Since 2.24

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.

isTuple

variantTypeIsTuple

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a VariantType

-> m Bool

Returns: True if type is a tuple type

Since 2.24

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.

isVariant

variantTypeIsVariant

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a VariantType

-> m Bool

Returns: True if type is the variant type

Since 2.24

Determines if the given type is the variant type.

key

variantTypeKey

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a dictionary entry VariantType

-> m VariantType

Returns: the key type of the dictionary entry

Since 2.24

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 variantTypeFirst.

nItems

variantTypeNItems

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a tuple or dictionary entry VariantType

-> m Word64

Returns: the number of items in type

Since 2.24

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.

new

variantTypeNew

Arguments

:: (HasCallStack, MonadIO m)

=> Text

typeString: a valid GVariant type string

-> m VariantType

Returns: a new VariantType

Creates a new VariantType corresponding to the type string given by typeString. It is appropriate to call variantTypeFree on the return value.

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

Since: 2.24

newArray

variantTypeNewArray

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

element: a VariantType

-> m VariantType

Returns: a new array VariantType

Since 2.24

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

It is appropriate to call variantTypeFree on the return value.

newDictEntry

variantTypeNewDictEntry

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

key: a basic VariantType

-> VariantType

value: a VariantType

-> m VariantType

Returns: a new dictionary entry VariantType

Since 2.24

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 variantTypeFree on the return value.

newMaybe

variantTypeNewMaybe

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

element: a VariantType

-> m VariantType

Returns: a new maybe VariantType

Since 2.24

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

It is appropriate to call variantTypeFree on the return value.

newTuple

variantTypeNewTuple

Arguments

:: (HasCallStack, MonadIO m)

=> [VariantType]

items: an array of GVariantTypes, one for each item

-> m VariantType

Returns: a new tuple VariantType

Since 2.24

Constructs a new tuple type, from items.

length is the number of items in items, or -1 to indicate that items is Nothing-terminated.

It is appropriate to call variantTypeFree on the return value.

next

variantTypeNext

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a VariantType from a previous call

-> m VariantType

Returns: the next VariantType after type, or Nothing

Since 2.24

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

type must be the result of a previous call to variantTypeFirst or variantTypeNext.

If called on the key type of a dictionary entry then this call returns the value type. If called on the value type of a dictionary entry then this call returns Nothing.

For tuples, Nothing is returned when type is the last item in a tuple.

stringGetDepth_

variantTypeStringGetDepth_ :: (HasCallStack, MonadIO m) => Text -> m Word64

No description available in the introspection data.

stringIsValid

variantTypeStringIsValid

Arguments

:: (HasCallStack, MonadIO m)

=> Text

typeString: a pointer to any string

-> m Bool

Returns: True if typeString is exactly one valid type string

Since 2.24

Checks if typeString is a valid GVariant type string. This call is equivalent to calling variantTypeStringScan and confirming that the following character is a nul terminator.

stringScan

variantTypeStringScan

Arguments

:: (HasCallStack, MonadIO m)

=> Text

string: a pointer to any string

-> Maybe Text

limit: the end of string, or Nothing

-> m (Bool, Text)

Returns: True if a valid type string was found

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.

If a valid type string is found, endptr is updated to point to the first character past the end of the string that was found and True is returned.

If there is no valid type string starting at string, or if the type string does not end before limit then False is returned.

For the simple case of checking if a string is a valid type string, see variantTypeStringIsValid.

Since: 2.24

value

variantTypeValue

Arguments

:: (HasCallStack, MonadIO m)

=> VariantType

type: a dictionary entry VariantType

-> m VariantType

Returns: the value type of the dictionary entry

Since 2.24

Determines the value type of a dictionary entry type.

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