## GVariantType GVariantType — introduction to the GVariant type system |

## Synopsis

    #include <glib.h>

                        GVariantType;
    #define             G_VARIANT_TYPE_BOOLEAN
    #define             G_VARIANT_TYPE_BYTE
    #define             G_VARIANT_TYPE_INT16
    #define             G_VARIANT_TYPE_UINT16
    #define             G_VARIANT_TYPE_INT32
    #define             G_VARIANT_TYPE_UINT32
    #define             G_VARIANT_TYPE_INT64
    #define             G_VARIANT_TYPE_UINT64
    #define             G_VARIANT_TYPE_HANDLE
    #define             G_VARIANT_TYPE_DOUBLE
    #define             G_VARIANT_TYPE_STRING
    #define             G_VARIANT_TYPE_OBJECT_PATH
    #define             G_VARIANT_TYPE_SIGNATURE
    #define             G_VARIANT_TYPE_VARIANT
    #define             G_VARIANT_TYPE_ANY
    #define             G_VARIANT_TYPE_BASIC
    #define             G_VARIANT_TYPE_MAYBE
    #define             G_VARIANT_TYPE_ARRAY
    #define             G_VARIANT_TYPE_TUPLE
    #define             G_VARIANT_TYPE_UNIT
    #define             G_VARIANT_TYPE_DICT_ENTRY
    #define             G_VARIANT_TYPE_DICTIONARY
    #define             G_VARIANT_TYPE_STRING_ARRAY
    #define             G_VARIANT_TYPE_BYTESTRING
    #define             G_VARIANT_TYPE_BYTESTRING_ARRAY

    #define             G_VARIANT_TYPE                      (type_string)
    void                g_variant_type_free                 (GVariantType *type);
    GVariantType *                   g_variant_type_copy    (const GVariantType *type);
    GVariantType *                   g_variant_type_new     (const gchar *type_string);

    gboolean            g_variant_type_string_is_valid      (const gchar *type_string);
    gboolean            g_variant_type_string_scan          (const gchar *string,
                                                             const gchar *limit,
                                                             const gchar **endptr);
    gsize               g_variant_type_get_string_length    (const GVariantType *type);
    const gchar *                    g_variant_type_peek_string
                                                            (const GVariantType *type);
    gchar *                          g_variant_type_dup_string
                                                            (const GVariantType *type);

    gboolean            g_variant_type_is_definite          (const GVariantType *type);
    gboolean            g_variant_type_is_container         (const GVariantType *type);
    gboolean            g_variant_type_is_basic             (const GVariantType *type);
    gboolean            g_variant_type_is_maybe             (const GVariantType *type);
    gboolean            g_variant_type_is_array             (const GVariantType *type);
    gboolean            g_variant_type_is_tuple             (const GVariantType *type);
    gboolean            g_variant_type_is_dict_entry        (const GVariantType *type);
    gboolean            g_variant_type_is_variant           (const GVariantType *type);

    guint               g_variant_type_hash                 (gconstpointer type);
    gboolean            g_variant_type_equal                (gconstpointer type1,
                                                             gconstpointer type2);
    gboolean            g_variant_type_is_subtype_of        (const GVariantType *type,
                                                             const GVariantType *supertype);

    GVariantType *                   g_variant_type_new_maybe
                                                            (const GVariantType *element);
    GVariantType *                   g_variant_type_new_array
                                                            (const GVariantType *element);
    GVariantType *                   g_variant_type_new_tuple
                                                            (const GVariantType * const *items,
                                                             gint length);
    GVariantType *                   g_variant_type_new_dict_entry
                                                            (const GVariantType *key,
                                                             const GVariantType *value);

    const GVariantType *             g_variant_type_element (const GVariantType *type);
    gsize               g_variant_type_n_items              (const GVariantType *type);
    const GVariantType *             g_variant_type_first   (const GVariantType *type);
    const GVariantType *             g_variant_type_next    (const GVariantType *type);
    const GVariantType *             g_variant_type_key     (const GVariantType *type);
    const GVariantType *             g_variant_type_value   (const GVariantType *type);

## Description

This section introduces the GVariant type system. It is based, in large part, on the DBus type system, with two major changes and some minor lifting of restrictions. The DBus specification, therefore, provides a significant amount of information that is useful when working with GVariant.

The first major change with respect to the DBus 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 DBus. For example, it is possible to speak of "an array of any type" in GVariant, where the DBus 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 DBus, 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 DBus. Note, however: DBus 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 DBus 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, `g_variant_get_type()` will never return an indefinite type, but calling `g_variant_is_a()` with an indefinite type may return `TRUE`. For example, you can not 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).

A detailed description of GVariant type strings is given here:

### 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 `g_variant_type_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 is "`a(aa(ui)(qna{ya(yd)}))`".

The meaning of each of the characters is as follows:

Character | Meaning
`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 DBus 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 DBus object path.
`g` | the type string of `G_VARIANT_TYPE_STRING`; a string in the form of a DBus 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 32 bit signed 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.

## Details

### GVariantType

    typedef struct _GVariantType GVariantType;

A type in the GVariant type system.

Two types may not be compared by value; use `g_variant_type_equal()` or `g_variant_type_is_subtype()`. May be copied using `g_variant_type_copy()` and freed using `g_variant_type_free()`.

### G_VARIANT_TYPE_BOOLEAN

    #define G_VARIANT_TYPE_BOOLEAN              ((const GVariantType *) "b")

The type of a value that can be either `TRUE` or `FALSE`.

### G_VARIANT_TYPE_BYTE

    #define G_VARIANT_TYPE_BYTE                 ((const GVariantType *) "y")

The type of an integer value that can range from 0 to 255.

### G_VARIANT_TYPE_INT16

    #define G_VARIANT_TYPE_INT16                ((const GVariantType *) "n")

The type of an integer value that can range from -32768 to 32767.

### G_VARIANT_TYPE_UINT16

    #define G_VARIANT_TYPE_UINT16               ((const GVariantType *) "q")

The type of an integer value that can range from 0 to 65535. There were about this many people living in Toronto in the 1870s.

### G_VARIANT_TYPE_INT32

    #define G_VARIANT_TYPE_INT32                ((const GVariantType *) "i")

The type of an integer value that can range from -2147483648 to 2147483647.

### G_VARIANT_TYPE_UINT32

    #define G_VARIANT_TYPE_UINT32               ((const GVariantType *) "u")

The type of an integer value that can range from 0 to 4294967295. That's one number for everyone who was around in the late 1970s.

### G_VARIANT_TYPE_INT64

    #define G_VARIANT_TYPE_INT64                ((const GVariantType *) "x")

The type of an integer value that can range from -9223372036854775808 to 9223372036854775807.

### G_VARIANT_TYPE_UINT64

    #define G_VARIANT_TYPE_UINT64               ((const GVariantType *) "t")

The type of an integer value that can range from 0 to 18446744073709551616. That's a really big number, but a Rubik's cube can have a bit more than twice as many possible positions.

### G_VARIANT_TYPE_HANDLE

    #define G_VARIANT_TYPE_HANDLE               ((const GVariantType *) "h")

The type of a 32bit signed integer value, that by convention, is used as an index into an array of file descriptors that are sent alongside a DBus message.

If you are not interacting with DBus, then there is no reason to make use of this type.

### G_VARIANT_TYPE_DOUBLE

    #define G_VARIANT_TYPE_DOUBLE               ((const GVariantType *) "d")

The type of a double precision IEEE754 floating point number. These guys go up to about 1.80e308 (plus and minus) but miss out on some numbers in between. In any case, that's far greater than the estimated number of fundamental particles in the observable universe.

### G_VARIANT_TYPE_STRING

    #define G_VARIANT_TYPE_STRING               ((const GVariantType *) "s")

The type of a string. "" is a string. `NULL` is not a string.

### G_VARIANT_TYPE_OBJECT_PATH

    #define G_VARIANT_TYPE_OBJECT_PATH          ((const GVariantType *) "o")

The type of a DBus object reference. These are strings of a specific format used to identify objects at a given destination on the bus.

If you are not interacting with DBus, then there is no reason to make use of this type. If you are, then the DBus specification contains a precise description of valid object paths.

### G_VARIANT_TYPE_SIGNATURE

    #define G_VARIANT_TYPE_SIGNATURE            ((const GVariantType *) "g")

The type of a DBus type signature. These are strings of a specific format used as type signatures for DBus methods and messages.

If you are not interacting with DBus, then there is no reason to make use of this type. If you are, then the DBus specification contains a precise description of valid signature strings.

### G_VARIANT_TYPE_VARIANT

    #define G_VARIANT_TYPE_VARIANT              ((const GVariantType *) "v")

The type of a box that contains any other value (including another variant).

### G_VARIANT_TYPE_ANY

    #define G_VARIANT_TYPE_ANY                  ((const GVariantType *) "*")

An indefinite type that is a supertype of every type (including itself).

### G_VARIANT_TYPE_BASIC

    #define G_VARIANT_TYPE_BASIC                ((const GVariantType *) "?")

An indefinite type that is a supertype of every basic (ie: non-container) type.

### G_VARIANT_TYPE_MAYBE

    #define G_VARIANT_TYPE_MAYBE                ((const GVariantType *) "m*")

An indefinite type that is a supertype of every maybe type.

### G_VARIANT_TYPE_ARRAY

    #define G_VARIANT_TYPE_ARRAY                ((const GVariantType *) "a*")

An indefinite type that is a supertype of every array type.

### G_VARIANT_TYPE_TUPLE

    #define G_VARIANT_TYPE_TUPLE                ((const GVariantType *) "r")

An indefinite type that is a supertype of every tuple type, regardless of the number of items in the tuple.

### G_VARIANT_TYPE_UNIT

    #define G_VARIANT_TYPE_UNIT                 ((const GVariantType *) "()")

The empty tuple type. Has only one instance. Known also as "triv" or "void".

### G_VARIANT_TYPE_DICT_ENTRY

    #define G_VARIANT_TYPE_DICT_ENTRY           ((const GVariantType *) "{?*}")

An indefinite type that is a supertype of every dictionary entry type.

### G_VARIANT_TYPE_DICTIONARY

    #define G_VARIANT_TYPE_DICTIONARY           ((const GVariantType *) "a{?*}")

An indefinite type that is a supertype of every dictionary type -- that is, any array type that has an element type equal to any dictionary entry type.

### G_VARIANT_TYPE_STRING_ARRAY

    #define G_VARIANT_TYPE_STRING_ARRAY         ((const GVariantType *) "as")

The type of an array of strings.

### G_VARIANT_TYPE_BYTESTRING

    #define G_VARIANT_TYPE_BYTESTRING           ((const GVariantType *) "ay")

The type of an array of bytes. This type is commonly used to pass around strings that may not be valid utf8. In that case, the convention is that the nul terminator character should be included as the last character in the array.

### G_VARIANT_TYPE_BYTESTRING_ARRAY

    #define G_VARIANT_TYPE_BYTESTRING_ARRAY     ((const GVariantType *) "aay")

The type of an array of byte strings (an array of arrays of bytes).

### G_VARIANT_TYPE()

    #define             G_VARIANT_TYPE(type_string)

Converts a string to a const GVariantType. Depending on the current debugging level, this function may perform a runtime check to ensure that `string` is a valid GVariant type string.

It is always a programmer error to use this macro with an invalid type string.

Since 2.24

`type_string` : | a well-formed GVariantType type string

### g_variant_type_free ()

    void                g_variant_type_free                 (GVariantType *type);

Frees a GVariantType that was allocated with `g_variant_type_copy()`, `g_variant_type_new()` or one of the container type constructor functions.

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

Since 2.24

`type` : | a GVariantType, or `NULL`

### g_variant_type_copy ()

    GVariantType *                   g_variant_type_copy    (const GVariantType *type);

Makes a copy of a GVariantType. It is appropriate to call `g_variant_type_free()` on the return value. `type` may not be `NULL`.

Since 2.24

`type` : | a GVariantType
Returns : | a new GVariantType

### g_variant_type_new ()

    GVariantType *                   g_variant_type_new     (const gchar *type_string);

Creates a new GVariantType corresponding to the type string given by `type_string`. It is appropriate to call `g_variant_type_free()` on the return value.

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

`type_string` : | a valid GVariant type string
Returns : | a new GVariantType

Since 2.24

### g_variant_type_string_is_valid ()

    gboolean            g_variant_type_string_is_valid      (const gchar *type_string);

Checks if `type_string` is a valid GVariant type string. This call is equivalent to calling `g_variant_type_string_scan()` and confirming that the following character is a nul terminator.

Since 2.24

`type_string` : | a pointer to any string
Returns : | `TRUE` if `type_string` is exactly one valid type string

### g_variant_type_string_scan ()

    gboolean            g_variant_type_string_scan          (const gchar *string,
                                                             const gchar *limit,
                                                             const gchar **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.

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 `g_variant_type_string_is_valid()`.

`string` : | a pointer to any string
`limit` : | the end of `string`, or `NULL`
`endptr` : | location to store the end pointer, or `NULL`
Returns : | `TRUE` if a valid type string was found

Since 2.24

### g_variant_type_get_string_length ()

    gsize               g_variant_type_get_string_length    (const GVariantType *type);

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 2.24

`type` : | a GVariantType
Returns : | the length of the corresponding type string

### g_variant_type_peek_string ()

    const gchar *                    g_variant_type_peek_string
                                                            (const GVariantType *type);

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 2.24

`type` : | a GVariantType
Returns : | the corresponding type string (not nul-terminated)

### g_variant_type_dup_string ()

    gchar *                          g_variant_type_dup_string
                                                            (const GVariantType *type);

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

Since 2.24

`type` : | a GVariantType
Returns : | the corresponding type string

### g_variant_type_is_definite ()

    gboolean            g_variant_type_is_definite          (const GVariantType *type);

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 `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 2.24

`type` : | a GVariantType
Returns : | `TRUE` if `type` is definite

### g_variant_type_is_container ()

    gboolean            g_variant_type_is_container         (const GVariantType *type);

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 2.24

`type` : | a GVariantType
Returns : | `TRUE` if `type` is a container type

### g_variant_type_is_basic ()

    gboolean            g_variant_type_is_basic             (const GVariantType *type);

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 2.24

`type` : | a GVariantType
Returns : | `TRUE` if `type` is a basic type

### g_variant_type_is_maybe ()

    gboolean            g_variant_type_is_maybe             (const GVariantType *type);

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 2.24

`type` : | a GVariantType
Returns : | `TRUE` if `type` is a maybe type

### g_variant_type_is_array ()

    gboolean            g_variant_type_is_array             (const GVariantType *type);

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 2.24

`type` : | a GVariantType
Returns : | `TRUE` if `type` is an array type

### g_variant_type_is_tuple ()

    gboolean            g_variant_type_is_tuple             (const GVariantType *type);

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 2.24

`type` : | a GVariantType
Returns : | `TRUE` if `type` is a tuple type

### g_variant_type_is_dict_entry ()

    gboolean            g_variant_type_is_dict_entry        (const GVariantType *type);

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 2.24

`type` : | a GVariantType
Returns : | `TRUE` if `type` is a dictionary entry type

### g_variant_type_is_variant ()

    gboolean            g_variant_type_is_variant           (const GVariantType *type);

Determines if the given `type` is the variant type.

Since 2.24

`type` : | a GVariantType
Returns : | `TRUE` if `type` is the variant type

### g_variant_type_hash ()

    guint               g_variant_type_hash                 (gconstpointer type);

Hashes `type`.

The argument type of `type` is only gconstpointer to allow use with GHashTable without function pointer casting. A valid GVariantType must be provided.

Since 2.24

`type` : | a GVariantType
Returns : | the hash value

### g_variant_type_equal ()

    gboolean            g_variant_type_equal                (gconstpointer type1,
                                                             gconstpointer type2);

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 `g_variant_type_is_subtype_of()`.

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

Since 2.24

`type1` : | a GVariantType
`type2` : | a GVariantType
Returns : | `TRUE` if `type1` and `type2` are exactly equal

### g_variant_type_is_subtype_of ()

    gboolean            g_variant_type_is_subtype_of        (const GVariantType *type,
                                                             const GVariantType *supertype);

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 2.24

`type` : | a GVariantType
`supertype` : | a GVariantType
Returns : | `TRUE` if `type` is a subtype of `supertype`

### g_variant_type_new_maybe ()

    GVariantType *                   g_variant_type_new_maybe
                                                            (const GVariantType *element);

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 2.24

`element` : | a GVariantType
Returns : | a new maybe GVariantType

### g_variant_type_new_array ()

    GVariantType *                   g_variant_type_new_array
                                                            (const GVariantType *element);

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 2.24

`element` : | a GVariantType
Returns : | a new array GVariantType

### g_variant_type_new_tuple ()

    GVariantType *                   g_variant_type_new_tuple
                                                            (const GVariantType * const *items,
                                                             gint length);

Constructs a new tuple type, from `items`.

`length` is the number of items in `items`, or -1 to indicate that `items` is `NULL`-terminated.

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

Since 2.24

`items` : | an array of GVariantTypes, one for each item
`length` : | the length of `items`, or -1
Returns : | a new tuple GVariantType

### g_variant_type_new_dict_entry ()

    GVariantType *                   g_variant_type_new_dict_entry
                                                            (const GVariantType *key,
                                                             const GVariantType *value);

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 2.24

`key` : | a basic GVariantType
`value` : | a GVariantType
Returns : | a new dictionary entry GVariantType

### g_variant_type_element ()

    const GVariantType *             g_variant_type_element (const GVariantType *type);

Determines the element type of an array or maybe type.

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

Since 2.24

`type` : | an array or maybe GVariantType
Returns : | the element type of `type`

### g_variant_type_n_items ()

    gsize               g_variant_type_n_items              (const GVariantType *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 type `G_VARIANT_TYPE_TUPLE`.

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

Since 2.24

`type` : | a tuple or dictionary entry GVariantType
Returns : | the number of items in `type`

### g_variant_type_first ()

    const GVariantType *             g_variant_type_first   (const GVariantType *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 type `G_VARIANT_TYPE_TUPLE`.

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

`NULL` is returned in case of `type` being `G_VARIANT_TYPE_UNIT`.

This call, together with `g_variant_type_next()` provides an iterator interface over tuple and dictionary entry types.

Since 2.24

`type` : | a tuple or dictionary entry GVariantType
Returns : | the first item type of `type`, or `NULL`

### g_variant_type_next ()

    const GVariantType *             g_variant_type_next    (const GVariantType *type);

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

`type` must be the result of a previous call to `g_variant_type_first()` or `g_variant_type_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 `type` is the last item in a tuple.

Since 2.24

`type` : | a GVariantType from a previous call
Returns : | the next GVariantType after `type`, or `NULL`

### g_variant_type_key ()

    const GVariantType *             g_variant_type_key     (const GVariantType *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 `g_variant_type_first()`.

Since 2.24

`type` : | a dictionary entry GVariantType
Returns : | the key type of the dictionary entry

### g_variant_type_value ()

    const GVariantType *             g_variant_type_value   (const GVariantType *type);

Determines the value type of a dictionary entry type.

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

Since 2.24

`type` : | a dictionary entry GVariantType
Returns : | the value type of the dictionary entry

## See Also

GVariantType, GVariant