Editing GObject (section)

===Fundamental types===
Types that do not have any associated [[class (programming)|class]]es are called ''non-classed''. These types, together with all types that correspond to some form of [[root class]], are known as ''fundamental types'': the types from which all other types are derived. These make up a relatively closed set, but although the average user is not expected to create their own fundamental types, the possibility does exist and has been exploited to create custom [[class hierarchy|class hierarchies]] &mdash; i.e., class hierarchies not based on the <code>GObject</code> class.

As of GLib 2.9.2,<ref>{{cite web|url=https://developer.gnome.org/gobject/stable|title=GObject Reference Manual - Stable}}</ref> the ''non-classed'' built-in fundamental types are:
* an empty type, corresponding to C's <code>void</code> (<code>G_TYPE_NONE</code>);
* types corresponding to C's signed and unsigned <code>char</code>, <code>int</code>, <code>long</code>, and 64-bit integers (<code>G_TYPE_CHAR</code>, <code>G_TYPE_UCHAR</code>, <code>G_TYPE_INT</code>, <code>G_TYPE_UINT</code>, <code>G_TYPE_LONG</code>, <code>G_TYPE_ULONG</code>, <code>G_TYPE_INT64</code>, and <code>G_TYPE_UINT64</code>);
* a Boolean type (<code>G_TYPE_BOOLEAN</code>);
* an enumeration type and a “flags” type, both corresponding to C's <code>enum</code> type, but differing in that the latter is only used for [[bit field]]s (<code>G_TYPE_ENUM</code> and <code>G_TYPE_FLAGS</code>);
* types for single- and double-precision [[IEEE float]]s, corresponding to C's <code>float</code> and <code>double</code> (<code>G_TYPE_FLOAT</code> and <code>G_TYPE_DOUBLE</code>);
* a string type, corresponding to C's <code>char *</code> (<code>G_TYPE_STRING</code>);
* an opaque pointer type, corresponding to C's <code>void *</code> (<code>G_TYPE_POINTER</code>).

The ''classed'' built-in fundamental types are:
* a base class type for instances of <code>GObject</code>, the root of the standard class inheritance tree (<code>G_TYPE_OBJECT</code>)
* a base interface type, analogous to the base class type but representing the root of the standard ''interface'' inheritance tree (<code>G_TYPE_INTERFACE</code>)
* a type for [[Boxed type|boxed]] structures, which are used to wrap simple value objects or foreign objects in reference-counted “boxes” (<code>G_TYPE_BOXED</code>)
* a type for “parameter specification objects,” which are used in GObject to describe [[metadata]] for object properties (<code>G_TYPE_PARAM</code>).

Types that can be instantiated automatically by the type system are called ''instantiable''. An important characteristic of these types is that the first bytes of any instance always contain a pointer to the ''class structure'' (a form of [[virtual table]]) associated to the type of the instance. For this reason, any instantiable type must be classed. Contrapositively, any non-classed type (such as ''integer'' or ''string'') must be non-instantiable. On the other hand, most classed types are instantiable, but some, such as interface types, are not.