Type System

This page describes the range of possible values that can be represented by a GVariant instance.

GVariant has a strong dynamic type system. Every GVariant instance has a type.

The possible types follow. This list is an exhaustive recursive definition of valid types (ie: no junk, no confusion).

  • boolean
  • byte
  • signed and unsigned 16, 32 and 64 bit integer
  • double (and maybe single) precision floating point
  • arbitrary precision integer
  • string
  • type string
  • object path string
  • variant
  • array (or "list") of x (where x is any valid type)

  • n-tuple (or structure) composed of any n types

  • dictionary entry (essentially a key-value pair)
  • maybe x (where x is any valid type)

  • a tagged union over any n types

Type Strings

Each type has an associated type string that describes it.

A property of type strings is that, given a pointer to the start of a type string embedded in a larger string, the length of the type string can be determined. This allows for construction of structure and tagged union types without requiring a separator between the individual subtypes. It also allows unambiguous construction of maybe and array type strings with a simple prefix.

The following is a list of all of the valid type strings.

Base Types

  • b - boolean

  • y - byte

  • n - signed 16 bit integer

  • q - unsigned 16 bit integer

  • i - signed 32 bit integer

  • u - unsigned 32 bit integer

  • x - signed 64 bit integer

  • t - unsigned 64 bit integer

  • f - single precision floating point (maybe)

  • d - double precision floating point

  • s - string

  • o - object path

  • g - type string

  • v - variant

Type Constructors

In the following list, a single underscore _ represents any valid type string. A dash - represents any valid one-character type string except for v. An underscore followed by a plus _+ indicates the concatenation of one or more valid type strings.

  • a_ - array (or list)

  • m_ - maybe

  • (_+) - n-tuple (or structure)

  • [_+] - tagged union

  • {-_} - dictionary entry

Valid Values

Boolean

A boolean value may be either false or true.

Byte

A byte may be any value between 0 and 255 inclusive.

(Un)signed 16/32/64bit Integers

A 16bit signed integer ranges from -32768 to 32767 inclusive. A 16bit unsigned integer ranges from 0 to 65535 inclusive.

A 32bit signed integer ranges from -2147483648 to 2147483647 inclusive. A 32bit unsigned integer ranges from 0 to 4294967296 inclusive.

A 64bit signed integer ranges from -9223372036854775808 to 9223372036854775807 inclusive. A 64bit unsigned integer ranges from 0 to 18446744073709551615 inclusive.

Floating Point Types

Floating point types range over the values specified in IEEE754, including infinities, positive and negative zeros and multiple different representations of NaN.

String

The string type ranges over valid utf-8 encodings of any length. Strings may not contain zero bytes.

Type String

The type string type ranges over all valid type strings (as described in the "Type Strings" section of this document).

Object Path

The object path type ranges over all valid DBus object paths. It consists of a number of segments, separated by '/' delimiters. Each segment may only contain the ASCII characters A-Z, a-z, 0-9 and _. The first segment must be empty and no other segment may be empty.

Variant

The value of a variant type is a pair of (type string, value). The type string may be any valid type string and the value may be any valid value of the type corresponding to that type string.

Array

The type "Array of _" ranges over range(_)* (where * is the Kleene closure operator).

Maybe

The type "Maybe _" ranges over the following possible values:

  • Nothing
  • Just x (where x is a member of the range of _)

Structure

The type "Structure of t0, t1, t2... tn" ranges over the cross product of the ranges of the types t0, t1, t2... tn.

Tagged Union

The type "Tagged union of t0, t1, t2... tn" ranges over the disjoint union of the ranges of the types t0, t1, t2... tn.

Dictionary Entry

The type "Dictionary Entry from k to v" ranges over the cross product of k × v.

Note that k is constrained to be a base type (and not a variant).

Projects/GLib/GVariant/Types (last edited 2013-12-03 17:48:31 by WilliamJonMcCann)