GLib.VariantType - Structures - GLib 2.0 (original) (raw)
Fields¶
None
Methods¶
| class | checked_ (type_string) |
|---|---|
| class | new (type_string) |
| class | new_array (element) |
| class | new_dict_entry (key, value) |
| class | new_maybe (element) |
| class | new_tuple (items) |
| class | string_get_depth_ (type_string) |
| class | string_is_valid (type_string) |
| class | string_scan (string, limit) |
| copy () | |
| dup_string () | |
| element () | |
| equal (type2) | |
| first () | |
| free () | |
| get_string_length () | |
| hash () | |
| is_array () | |
| is_basic () | |
| is_container () | |
| is_definite () | |
| is_dict_entry () | |
| is_maybe () | |
| is_subtype_of (supertype) | |
| is_tuple () | |
| is_variant () | |
| key () | |
| n_items () | |
| next () | |
| value () |
Details¶
class GLib.VariantType¶
A type in the [type`GLib`.Variant] type system.
[type`GLib`.Variant] types are represented as strings, but have a strict syntax described below. All [type`GLib`.VariantType]s passed to GLib must be valid, and they are typically expected to be static (i.e. not provided by user input) as they determine how binary [type`GLib`.Variant] data is interpreted.
To convert a static string to a [type`GLib`.VariantType] in C, use the [func`GLib`.VARIANT_TYPE] casting macro. When GLib is compiled with checks enabled, it will validate the type. To check if an arbitrary string is a valid [type`GLib`.VariantType], use [func`GLib`.VariantType.string_is_valid].
GLib.Variant Type System
This section introduces the [type`GLib`.Variant] type system. It is based, in large part, on the D-Bus type system, with two major changes and some minor lifting of restrictions. TheD-Bus specification, therefore, provides a significant amount of information that is useful when working with [type`GLib`.Variant].
The first major change with respect to the D-Bus type system is the introduction of maybe (or ‘nullable’) types. Any type in [type`GLib`.Variant] 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 [type`GLib`.Variant] 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 [type`GLib`.Variant], 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, [type`GLib`.Variant] 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. [type`GLib`.Variant] deals with single values directly so [type`GLib`.Variant] type strings always describe the type of exactly one value. This means that a D-Bus signature string is generally not a valid [type`GLib`.Variant] 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, [method`GLib`.Variant.get_type] will never return an indefinite type, but calling [method`GLib`.Variant.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 GTK, no object that has the type of GtkWidget can exist (since GtkWidget is an abstract class), but a GtkWindowcan certainly be instantiated, and you would say that a GtkWindow is aGtkWidget (since GtkWindow is a subclass of GtkWidget).
Two types may not be compared by value; use [method`GLib`.VariantType.equal] or [method`GLib`.VariantType.is_subtype_of] May be copied using [method`GLib`.VariantType.copy] and freed using [method`GLib`.VariantType.free].
GLib.Variant Type Strings
A [type`GLib`.Variant] type string can be any of the following:
- any basic type string (listed below)
v,ror*- one of the characters
aorm, 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 [method`GLib`.VariantType.is_basic]) 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 isa(aa(ui)(qna{ya(yd)})). In order to not hit memory limits, [type`GLib`.Variant] 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 ofG_VARIANT_TYPE_BOOLEAN; a boolean value.y: the type string ofG_VARIANT_TYPE_BYTE; a byte.n: the type string ofG_VARIANT_TYPE_INT16; a signed 16 bit integer.q: the type string ofG_VARIANT_TYPE_UINT16; an unsigned 16 bit integer.i: the type string ofG_VARIANT_TYPE_INT32; a signed 32 bit integer.u: the type string ofG_VARIANT_TYPE_UINT32; an unsigned 32 bit integer.x: the type string ofG_VARIANT_TYPE_INT64; a signed 64 bit integer.t: the type string ofG_VARIANT_TYPE_UINT64; an unsigned 64 bit integer.h: the type string ofG_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 ofG_VARIANT_TYPE_DOUBLE; a double precision floating point value.s: the type string ofG_VARIANT_TYPE_STRING; a string.o: the type string ofG_VARIANT_TYPE_OBJECT_PATH; a string in the form of a D-Bus object path.g: the type string ofG_VARIANT_TYPE_SIGNATURE; a string in the form of a D-Bus type signature.?: the type string ofG_VARIANT_TYPE_BASIC; an indefinite type that is a supertype of any of the basic types.v: the type string ofG_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 stringai, 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 stringms, 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 ofG_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 stringa{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 ofG_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.
New in version 2.24.
classmethod checked_(type_string)[source]¶
Parameters:
type_string (str) –
Return type:
classmethod new(type_string)[source]¶
Parameters:
type_string (str) – a valid GVariant type string
Returns:
a new [type`GLib`.VariantType]
Return type:
Creates a new [type`GLib`.VariantType] corresponding to the type string given by type_string.
It is appropriate to call [method`GLib`.VariantType.free] on the return value.
It is a programmer error to call this function with an invalid type string. Use [func`GLib`.VariantType.string_is_valid] if you are unsure.
New in version 2.24.
classmethod new_array(element)[source]¶
Parameters:
element (GLib.VariantType) – an element type
Returns:
a new array type
Return type:
Constructs the type corresponding to an array of elements of the type type.
It is appropriate to call [method`GLib`.VariantType.first] on the return value.
classmethod new_dict_entry(key, value)[source]¶
Parameters:
- key (GLib.VariantType) – a basic type to use for the key
- value (GLib.VariantType) – a type to use for the value
Returns:
a new dictionary entry type
Return type:
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 [method`GLib`.VariantType.free] on the return value.
classmethod new_maybe(element)[source]¶
Parameters:
element (GLib.VariantType) – an element type
Returns:
a new ‘maybe’ type
Return type:
Constructs the type corresponding to a ‘maybe’ instance containing type type or Nothing.
It is appropriate to call [method`GLib`.VariantType.free] on the return value.
classmethod new_tuple(items)[source]¶
Parameters:
items ([GLib.VariantType]) – an array of types, one for each item
Returns:
a new tuple type
Return type:
Constructs a new tuple type, from items.
length is the number of items in items, or -1 to indicate thatitems is NULL-terminated.
It is appropriate to call [method`GLib`.VariantType.free] on the return value.
classmethod string_get_depth_(type_string)[source]¶
Parameters:
type_string (str) –
Return type:
classmethod string_is_valid(type_string)[source]¶
Parameters:
type_string (str) – a pointer to any string
Returns:
true if type_string is exactly one valid type string
Return type:
Checks if type_string is a validGVariant type string.
This call is equivalent to calling [func`GLib`.VariantType.string_scan] and confirming that the following character is a nul terminator.
classmethod string_scan(string, limit)[source]¶
Parameters:
Returns:
true if a valid type string was found
endptr:
location to store the end pointer
Return type:
Scan for a single complete and valid GLib.Variant 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 Trueis 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 [func`GLib`.VariantType.string_is_valid].
New in version 2.24.
Returns:
a new [type`GLib`.VariantType]
Return type:
Makes a copy of a [type`GLib`.VariantType].
It is appropriate to call [method`GLib`.VariantType.free] on the return value.self may not be NULL.
Returns:
the corresponding type string
Return type:
Returns a newly-allocated copy of the type string corresponding to self.
The returned string is nul-terminated. It is appropriate to call [func`GLib`.free] on the return value.
Returns:
the element type of self
Return type:
Determines the element type of an array or ‘maybe’ type.
This function may only be used with array or ‘maybe’ types.
Parameters:
type2 (GLib.VariantType) – another type to compare
Returns:
true if self and type2 are exactly equal
Return type:
Compares self 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 [method`GLib`.VariantType.is_subtype_of].
The argument types of self and type2 are only gconstpointer to allow use with [type`GLib`.HashTable] without function pointer casting. For both arguments, a valid [type`GLib`.VariantType] must be provided.
Returns:
the first item type of self, or NULLif the type has no item types
Return type:
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 typeG_VARIANT_TYPE_TUPLE.
In the case of a dictionary entry type, this returns the type of the key.
NULL is returned in case of self being G_VARIANT_TYPE_UNIT.
This call, together with [method`GLib`.VariantType.next] provides an iterator interface over tuple and dictionary entry types.
Frees a [type`GLib`.VariantType] that was allocated with [method`GLib`.VariantType.copy], [ctor`GLib`.VariantType.new] or one of the container type constructor functions.
In the case that self is NULL, this function does nothing.
New in version 2.24.
Returns:
the length of the corresponding type string
Return type:
Returns the length of the type string corresponding to the given self.
This function must be used to determine the valid extent of the memory region returned by [method`GLib`.VariantType.peek_string].
Returns:
the hash value
Return type:
Hashes self.
The argument type of self is only gconstpointer to allow use with [type`GLib`.HashTable] without function pointer casting. A valid [type`GLib`.VariantType] must be provided.
Returns:
true if self is an array type
Return type:
Determines if the given self is an array type.
This is true if the type string for self 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.
Returns:
true if self is a basic type
Return type:
Determines if the given self 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 exceptG_VARIANT_TYPE_BASIC.
Returns:
true if self is a container type
Return type:
Determines if the given self 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.
Returns:
true if self is definite
Return type:
Determines if the given self is definite (ie: not indefinite).
A type is definite if its type string does not contain any indefinite type characters (*, ?, or r).
A [type`GLib`.Variant] instance may not have an indefinite type, so calling this function on the result of [method`GLib`.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 inFALSE being returned.
Returns:
true if self is a dictionary entry type
Return type:
Determines if the given self is a dictionary entry type.
This is true if the type string for self 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.
Returns:
true if self is a ‘maybe’ type
Return type:
Determines if the given self is a ‘maybe’ type.
This is true if the type string for self 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.
is_subtype_of(supertype)[source]¶
Parameters:
supertype (GLib.VariantType) – type of potential supertype
Returns:
true if self is a subtype of supertype
Return type:
Checks if self is a subtype of supertype.
This function returns true if self is a subtype of supertype. All types are considered to be subtypes of themselves. Aside from that, only indefinite types can have subtypes.
Returns:
true if self is a tuple type
Return type:
Determines if the given self is a tuple type.
This is true if the type string for self starts with a ( or if self isG_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.
Returns:
true if self is the variant type
Return type:
Determines if the given self is the variant type.
Returns:
the key type of the dictionary entry
Return type:
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 [method`GLib`.VariantType.first].
Returns:
the number of items in self
Return type:
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 typeG_VARIANT_TYPE_TUPLE.
In the case of a dictionary entry type, this function will always return 2.
Returns:
the next type after self, or NULL if there are no further types
Return type:
Determines the next item type of a tuple or dictionary entry type.
self must be the result of a previous call to [method`GLib`.VariantType.first] or [method`GLib`.VariantType.next].
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 NULL.
For tuples, NULL is returned when self is the last item in the tuple.
Returns:
the value type of the dictionary entry
Return type:
Determines the value type of a dictionary entry type.
This function may only be used with a dictionary entry type.