GParamSpec

GParamSpec — Metadata for parameter specifications

Synopsis

#include <glib-object.h>

#define             G_TYPE_IS_PARAM                     (type)
#define             G_PARAM_SPEC                        (pspec)
#define             G_IS_PARAM_SPEC                     (pspec)
#define             G_PARAM_SPEC_CLASS                  (pclass)
#define             G_IS_PARAM_SPEC_CLASS               (pclass)
#define             G_PARAM_SPEC_GET_CLASS              (pspec)
#define             G_PARAM_SPEC_TYPE                   (pspec)
#define             G_PARAM_SPEC_TYPE_NAME              (pspec)
#define             G_PARAM_SPEC_VALUE_TYPE             (pspec)
struct              GParamSpec;
struct              GParamSpecClass;
enum                GParamFlags;
#define             G_PARAM_READWRITE
#define             G_PARAM_STATIC_STRINGS
#define             G_PARAM_MASK
#define             G_PARAM_USER_SHIFT
GParamSpec *        g_param_spec_ref                    (GParamSpec *pspec);
void                g_param_spec_unref                  (GParamSpec *pspec);
void                g_param_spec_sink                   (GParamSpec *pspec);
GParamSpec *        g_param_spec_ref_sink               (GParamSpec *pspec);
void                g_param_value_set_default           (GParamSpec *pspec,
                                                         GValue *value);
gboolean            g_param_value_defaults              (GParamSpec *pspec,
                                                         GValue *value);
gboolean            g_param_value_validate              (GParamSpec *pspec,
                                                         GValue *value);
gboolean            g_param_value_convert               (GParamSpec *pspec,
                                                         const GValue *src_value,
                                                         GValue *dest_value,
                                                         gboolean strict_validation);
gint                g_param_values_cmp                  (GParamSpec *pspec,
                                                         const GValue *value1,
                                                         const GValue *value2);
const gchar *       g_param_spec_get_name               (GParamSpec *pspec);
const gchar *       g_param_spec_get_nick               (GParamSpec *pspec);
const gchar *       g_param_spec_get_blurb              (GParamSpec *pspec);
gpointer            g_param_spec_get_qdata              (GParamSpec *pspec,
                                                         GQuark quark);
void                g_param_spec_set_qdata              (GParamSpec *pspec,
                                                         GQuark quark,
                                                         gpointer data);
void                g_param_spec_set_qdata_full         (GParamSpec *pspec,
                                                         GQuark quark,
                                                         gpointer data,
                                                         GDestroyNotify destroy);
gpointer            g_param_spec_steal_qdata            (GParamSpec *pspec,
                                                         GQuark quark);
GParamSpec *        g_param_spec_get_redirect_target    (GParamSpec *pspec);
gpointer            g_param_spec_internal               (GType param_type,
                                                         const gchar *name,
                                                         const gchar *nick,
                                                         const gchar *blurb,
                                                         GParamFlags flags);
struct              GParamSpecTypeInfo;
GType               g_param_type_register_static        (const gchar *name,
                                                         const GParamSpecTypeInfo *pspec_info);
                    GParamSpecPool;
GParamSpecPool *    g_param_spec_pool_new               (gboolean type_prefixing);
void                g_param_spec_pool_insert            (GParamSpecPool *pool,
                                                         GParamSpec *pspec,
                                                         GType owner_type);
void                g_param_spec_pool_remove            (GParamSpecPool *pool,
                                                         GParamSpec *pspec);
GParamSpec *        g_param_spec_pool_lookup            (GParamSpecPool *pool,
                                                         const gchar *param_name,
                                                         GType owner_type,
                                                         gboolean walk_ancestors);
GParamSpec **       g_param_spec_pool_list              (GParamSpecPool *pool,
                                                         GType owner_type,
                                                         guint *n_pspecs_p);
GList *             g_param_spec_pool_list_owned        (GParamSpecPool *pool,
                                                         GType owner_type);

Description

GParamSpec is an object structure that encapsulates the metadata required to specify parameters, such as e.g. GObject properties.

Parameter names need to start with a letter (a-z or A-Z). Subsequent characters can be letters, numbers or a '-'. All other characters are replaced by a '-' during construction. The result of this replacement is called the canonical name of the parameter.

Details

G_TYPE_IS_PARAM()

#define G_TYPE_IS_PARAM(type)		(G_TYPE_FUNDAMENTAL (type) == G_TYPE_PARAM)

Checks whether type "is a" G_TYPE_PARAM.

type :

a GType ID

G_PARAM_SPEC()

#define G_PARAM_SPEC(pspec)		(G_TYPE_CHECK_INSTANCE_CAST ((pspec), G_TYPE_PARAM, GParamSpec))

Casts a derived GParamSpec object (e.g. of type GParamSpecInt) into a GParamSpec object.

pspec :

a valid GParamSpec

G_IS_PARAM_SPEC()

#define G_IS_PARAM_SPEC(pspec)		(G_TYPE_CHECK_INSTANCE_TYPE ((pspec), G_TYPE_PARAM))

Checks whether pspec "is a" valid GParamSpec structure of type G_TYPE_PARAM or derived.

pspec :

a GParamSpec

G_PARAM_SPEC_CLASS()

#define G_PARAM_SPEC_CLASS(pclass)      (G_TYPE_CHECK_CLASS_CAST ((pclass), G_TYPE_PARAM, GParamSpecClass))

Casts a derived GParamSpecClass structure into a GParamSpecClass structure.

pclass :

a valid GParamSpecClass

G_IS_PARAM_SPEC_CLASS()

#define G_IS_PARAM_SPEC_CLASS(pclass)   (G_TYPE_CHECK_CLASS_TYPE ((pclass), G_TYPE_PARAM))

Checks whether pclass "is a" valid GParamSpecClass structure of type G_TYPE_PARAM or derived.

pclass :

a GParamSpecClass

G_PARAM_SPEC_GET_CLASS()

#define G_PARAM_SPEC_GET_CLASS(pspec) (G_TYPE_INSTANCE_GET_CLASS ((pspec), G_TYPE_PARAM, GParamSpecClass))

Retrieves the GParamSpecClass of a GParamSpec.

pspec :

a valid GParamSpec

G_PARAM_SPEC_TYPE()

#define G_PARAM_SPEC_TYPE(pspec) (G_TYPE_FROM_INSTANCE (pspec))

Retrieves the GType of this pspec.

pspec :

a valid GParamSpec

G_PARAM_SPEC_TYPE_NAME()

#define G_PARAM_SPEC_TYPE_NAME(pspec) (g_type_name (G_PARAM_SPEC_TYPE (pspec)))

Retrieves the GType name of this pspec.

pspec :

a valid GParamSpec

G_PARAM_SPEC_VALUE_TYPE()

#define G_PARAM_SPEC_VALUE_TYPE(pspec) (G_PARAM_SPEC (pspec)->value_type)

Retrieves the GType to initialize a GValue for this parameter.

pspec :

a valid GParamSpec

struct GParamSpec

struct GParamSpec {
  GTypeInstance  g_type_instance;

  gchar         *name;
  GParamFlags    flags;
  GType		 value_type;
  GType		 owner_type; /* class or interface using this property */
};

All other fields of the GParamSpec struct are private and should not be used directly.

GTypeInstance g_type_instance;

private GTypeInstance portion

gchar *name;

name of this parameter

GParamFlags flags;

GParamFlags flags for this parameter

GType value_type;

the GValue type for this parameter

GType owner_type;

GType type that uses (introduces) this paremeter

struct GParamSpecClass

struct GParamSpecClass {
  GTypeClass      g_type_class;

  GType		  value_type;

  void	        (*finalize)		(GParamSpec   *pspec);

  /* GParam methods */
  void          (*value_set_default)    (GParamSpec   *pspec,
					 GValue       *value);
  gboolean      (*value_validate)       (GParamSpec   *pspec,
					 GValue       *value);
  gint          (*values_cmp)           (GParamSpec   *pspec,
					 const GValue *value1,
					 const GValue *value2);
};

The class structure for the GParamSpec type. Normally, GParamSpec classes are filled by g_param_type_register_static().

GTypeClass g_type_class;

the parent class

GType value_type;

the GValue type for this parameter

finalize ()

The instance finalization function (optional), should chain up to the finalize method of the parent class.

value_set_default ()

Resets a value to the default value for this type (recommended, the default is g_value_reset()), see g_param_value_set_default().

value_validate ()

Ensures that the contents of value comply with the specifications set out by this type (optional), see g_param_value_set_validate().

values_cmp ()

Compares value1 with value2 according to this type (recommended, the default is memcmp()), see g_param_values_cmp().

enum GParamFlags

typedef enum {
  G_PARAM_READABLE            = 1 << 0,
  G_PARAM_WRITABLE            = 1 << 1,
  G_PARAM_CONSTRUCT	      = 1 << 2,
  G_PARAM_CONSTRUCT_ONLY      = 1 << 3,
  G_PARAM_LAX_VALIDATION      = 1 << 4,
  G_PARAM_STATIC_NAME	      = 1 << 5,
#ifndef G_DISABLE_DEPRECATED
  G_PARAM_PRIVATE	      = G_PARAM_STATIC_NAME,
#endif
  G_PARAM_STATIC_NICK	      = 1 << 6,
  G_PARAM_STATIC_BLURB	      = 1 << 7
} GParamFlags;

Through the GParamFlags flag values, certain aspects of parameters can be configured.

G_PARAM_READABLE

the parameter is readable

G_PARAM_WRITABLE

the parameter is writable

G_PARAM_CONSTRUCT

the parameter will be set upon object construction

G_PARAM_CONSTRUCT_ONLY

the parameter will only be set upon object construction

G_PARAM_LAX_VALIDATION

upon parameter conversion (see g_param_value_convert()) strict validation is not required

G_PARAM_STATIC_NAME

the string used as name when constructing the parameter is guaranteed to remain valid and unmodified for the lifetime of the parameter. Since 2.8

G_PARAM_PRIVATE

internal

G_PARAM_STATIC_NICK

the string used as nick when constructing the parameter is guaranteed to remain valid and unmmodified for the lifetime of the parameter. Since 2.8

G_PARAM_STATIC_BLURB

the string used as blurb when constructing the parameter is guaranteed to remain valid and unmodified for the lifetime of the parameter. Since 2.8

G_PARAM_READWRITE

#define G_PARAM_READWRITE (G_PARAM_READABLE | G_PARAM_WRITABLE)

GParamFlags value alias for G_PARAM_READABLE | G_PARAM_WRITABLE.


G_PARAM_STATIC_STRINGS

#define G_PARAM_STATIC_STRINGS (G_PARAM_STATIC_NAME | G_PARAM_STATIC_NICK | G_PARAM_STATIC_BLURB)

GParamFlags value alias for G_PARAM_STATIC_NAME | G_PARAM_STATIC_NICK | G_PARAM_STATIC_BLURB.

Since 2.13.0


G_PARAM_MASK

#define G_PARAM_MASK		(0x000000ff)

Mask containing the bits of GParamSpec.flags which are reserved for GLib.


G_PARAM_USER_SHIFT

#define G_PARAM_USER_SHIFT (8)

Minimum shift count to be used for user defined flags, to be stored in GParamSpec.flags.


g_param_spec_ref ()

GParamSpec *        g_param_spec_ref                    (GParamSpec *pspec);

Increments the reference count of pspec.

pspec :

a valid GParamSpec

Returns :

the GParamSpec that was passed into this function

g_param_spec_unref ()

void                g_param_spec_unref                  (GParamSpec *pspec);

Decrements the reference count of a pspec.

pspec :

a valid GParamSpec

g_param_spec_sink ()

void                g_param_spec_sink                   (GParamSpec *pspec);

The initial reference count of a newly created GParamSpec is 1, even though no one has explicitly called g_param_spec_ref() on it yet. So the initial reference count is flagged as "floating", until someone calls g_param_spec_ref (pspec); g_param_spec_sink (pspec); in sequence on it, taking over the initial reference count (thus ending up with a pspec that has a reference count of 1 still, but is not flagged "floating" anymore).

pspec :

a valid GParamSpec

g_param_spec_ref_sink ()

GParamSpec *        g_param_spec_ref_sink               (GParamSpec *pspec);

Convenience function to ref and sink a GParamSpec.

pspec :

a valid GParamSpec

Returns :

the GParamSpec that was passed into this function

Since 2.10


g_param_value_set_default ()

void                g_param_value_set_default           (GParamSpec *pspec,
                                                         GValue *value);

Sets value to its default value as specified in pspec.

pspec :

a valid GParamSpec

value :

a GValue of correct type for pspec

g_param_value_defaults ()

gboolean            g_param_value_defaults              (GParamSpec *pspec,
                                                         GValue *value);

Checks whether value contains the default value as specified in pspec.

pspec :

a valid GParamSpec

value :

a GValue of correct type for pspec

Returns :

whether value contains the canonical default for this pspec

g_param_value_validate ()

gboolean            g_param_value_validate              (GParamSpec *pspec,
                                                         GValue *value);

Ensures that the contents of value comply with the specifications set out by pspec. For example, a GParamSpecInt might require that integers stored in value may not be smaller than -42 and not be greater than +42. If value contains an integer outside of this range, it is modified accordingly, so the resulting value will fit into the range -42 .. +42.

pspec :

a valid GParamSpec

value :

a GValue of correct type for pspec

Returns :

whether modifying value was necessary to ensure validity

g_param_value_convert ()

gboolean            g_param_value_convert               (GParamSpec *pspec,
                                                         const GValue *src_value,
                                                         GValue *dest_value,
                                                         gboolean strict_validation);

Transforms src_value into dest_value if possible, and then validates dest_value, in order for it to conform to pspec. If strict_validation is TRUE this function will only succeed if the transformed dest_value complied to pspec without modifications.

See also g_value_type_transformable(), g_value_transform() and g_param_value_validate().

pspec :

a valid GParamSpec

src_value :

souce GValue

dest_value :

destination GValue of correct type for pspec

strict_validation :

TRUE requires dest_value to conform to pspec without modifications

Returns :

TRUE if transformation and validation were successful, FALSE otherwise and dest_value is left untouched.

g_param_values_cmp ()

gint                g_param_values_cmp                  (GParamSpec *pspec,
                                                         const GValue *value1,
                                                         const GValue *value2);

Compares value1 with value2 according to pspec, and return -1, 0 or +1, if value1 is found to be less than, equal to or greater than value2, respectively.

pspec :

a valid GParamSpec

value1 :

a GValue of correct type for pspec

value2 :

a GValue of correct type for pspec

Returns :

-1, 0 or +1, for a less than, equal to or greater than result

g_param_spec_get_name ()

const gchar *       g_param_spec_get_name               (GParamSpec *pspec);

Get the name of a GParamSpec.

pspec :

a valid GParamSpec

Returns :

the name of pspec.

g_param_spec_get_nick ()

const gchar *       g_param_spec_get_nick               (GParamSpec *pspec);

Get the nickname of a GParamSpec.

pspec :

a valid GParamSpec

Returns :

the nickname of pspec.

g_param_spec_get_blurb ()

const gchar *       g_param_spec_get_blurb              (GParamSpec *pspec);

Get the short description of a GParamSpec.

pspec :

a valid GParamSpec

Returns :

the short description of pspec.

g_param_spec_get_qdata ()

gpointer            g_param_spec_get_qdata              (GParamSpec *pspec,
                                                         GQuark quark);

Gets back user data pointers stored via g_param_spec_set_qdata().

pspec :

a valid GParamSpec

quark :

a GQuark, naming the user data pointer

Returns :

the user data pointer set, or NULL

g_param_spec_set_qdata ()

void                g_param_spec_set_qdata              (GParamSpec *pspec,
                                                         GQuark quark,
                                                         gpointer data);

Sets an opaque, named pointer on a GParamSpec. The name is specified through a GQuark (retrieved e.g. via g_quark_from_static_string()), and the pointer can be gotten back from the pspec with g_param_spec_get_qdata(). Setting a previously set user data pointer, overrides (frees) the old pointer set, using NULL as pointer essentially removes the data stored.

pspec :

the GParamSpec to set store a user data pointer

quark :

a GQuark, naming the user data pointer

data :

an opaque user data pointer

g_param_spec_set_qdata_full ()

void                g_param_spec_set_qdata_full         (GParamSpec *pspec,
                                                         GQuark quark,
                                                         gpointer data,
                                                         GDestroyNotify destroy);

This function works like g_param_spec_set_qdata(), but in addition, a void (*destroy) (gpointer) function may be specified which is called with data as argument when the pspec is finalized, or the data is being overwritten by a call to g_param_spec_set_qdata() with the same quark.

pspec :

the GParamSpec to set store a user data pointer

quark :

a GQuark, naming the user data pointer

data :

an opaque user data pointer

destroy :

function to invoke with data as argument, when data needs to be freed

g_param_spec_steal_qdata ()

gpointer            g_param_spec_steal_qdata            (GParamSpec *pspec,
                                                         GQuark quark);

Gets back user data pointers stored via g_param_spec_set_qdata() and removes the data from pspec without invoking its destroy() function (if any was set). Usually, calling this function is only required to update user data pointers with a destroy notifier.

pspec :

the GParamSpec to get a stored user data pointer from

quark :

a GQuark, naming the user data pointer

Returns :

the user data pointer set, or NULL

g_param_spec_get_redirect_target ()

GParamSpec *        g_param_spec_get_redirect_target    (GParamSpec *pspec);

If the paramspec redirects operations to another paramspec, returns that paramspec. Redirect is used typically for providing a new implementation of a property in a derived type while preserving all the properties from the parent type. Redirection is established by creating a property of type GParamSpecOverride. See g_object_class_override_property() for an example of the use of this capability.

pspec :

a GParamSpec

Returns :

paramspec to which requests on this paramspec should be redirected, or NULL if none.

Since 2.4


g_param_spec_internal ()

gpointer            g_param_spec_internal               (GType param_type,
                                                         const gchar *name,
                                                         const gchar *nick,
                                                         const gchar *blurb,
                                                         GParamFlags flags);

Creates a new GParamSpec instance.

A property name consists of segments consisting of ASCII letters and digits, separated by either the '-' or '_' character. The first character of a property name must be a letter. Names which violate these rules lead to undefined behaviour.

When creating and looking up a GParamSpec, either separator can be used, but they cannot be mixed. Using '-' is considerably more efficient and in fact required when using property names as detail strings for signals.

Beyond the name, GParamSpecs have two more descriptive strings associated with them, the nick, which should be suitable for use as a label for the property in a property editor, and the blurb, which should be a somewhat longer description, suitable for e.g. a tooltip. The nick and blurb should ideally be localized.

param_type :

the GType for the property; must be derived from G_TYPE_PARAM

name :

the canonical name of the property

nick :

the nickname of the property

blurb :

a short description of the property

flags :

a combination of GParamFlags

Returns :

a newly allocated GParamSpec instance

struct GParamSpecTypeInfo

struct GParamSpecTypeInfo {
  /* type system portion */
  guint16         instance_size;                               /* obligatory */
  guint16         n_preallocs;                                 /* optional */
  void		(*instance_init) (GParamSpec   *pspec); /* optional */

  /* class portion */
  GType           value_type;				       /* obligatory */
  void          (*finalize)             (GParamSpec   *pspec); /* optional */
  void          (*value_set_default)    (GParamSpec   *pspec,  /* recommended */
					 GValue       *value);
  gboolean      (*value_validate)       (GParamSpec   *pspec,  /* optional */
					 GValue       *value);
  gint          (*values_cmp)           (GParamSpec   *pspec,  /* recommended */
					 const GValue *value1,
					 const GValue *value2);
};

This structure is used to provide the type system with the information required to initialize and destruct (finalize) a parameter's class and instances thereof. The initialized structure is passed to the g_param_type_register_static() The type system will perform a deep copy of this structure, so its memory does not need to be persistent across invocation of g_param_type_register_static().

guint16 instance_size;

Size of the instance (object) structure.

guint16 n_preallocs;

Prior to GLib 2.10, it specified the number of pre-allocated (cached) instances to reserve memory for (0 indicates no caching). Since GLib 2.10, it is ignored, since instances are allocated with the slice allocator now.

instance_init ()

Location of the instance initialization function (optional).

GType value_type;

The GType of values conforming to this GParamSpec

finalize ()

The instance finalization function (optional).

value_set_default ()

Resets a value to the default value for pspec (recommended, the default is g_value_reset()), see g_param_value_set_default().

value_validate ()

Ensures that the contents of value comply with the specifications set out by pspec (optional), see g_param_value_set_validate().

values_cmp ()

Compares value1 with value2 according to pspec (recommended, the default is memcmp()), see g_param_values_cmp().

g_param_type_register_static ()

GType               g_param_type_register_static        (const gchar *name,
                                                         const GParamSpecTypeInfo *pspec_info);

Registers name as the name of a new static type derived from G_TYPE_PARAM. The type system uses the information contained in the GParamSpecTypeInfo structure pointed to by info to manage the GParamSpec type and its instances.

name :

0-terminated string used as the name of the new GParamSpec type.

pspec_info :

The GParamSpecTypeInfo for this GParamSpec type.

Returns :

The new type identifier.

GParamSpecPool

typedef struct _GParamSpecPool GParamSpecPool;

A GParamSpecPool maintains a collection of GParamSpecs which can be quickly accessed by owner and name. The implementation of the GObject property system uses such a pool to store the GParamSpecs of the properties all object types.


g_param_spec_pool_new ()

GParamSpecPool *    g_param_spec_pool_new               (gboolean type_prefixing);

Creates a new GParamSpecPool.

If type_prefixing is TRUE, lookups in the newly created pool will allow to specify the owner as a colon-separated prefix of the property name, like "GtkContainer:border-width". This feature is deprecated, so you should always set type_prefixing to FALSE.

type_prefixing :

Whether the pool will support type-prefixed property names.

Returns :

a newly allocated GParamSpecPool.

g_param_spec_pool_insert ()

void                g_param_spec_pool_insert            (GParamSpecPool *pool,
                                                         GParamSpec *pspec,
                                                         GType owner_type);

Inserts a GParamSpec in the pool.

pool :

a GParamSpecPool.

pspec :

the GParamSpec to insert

owner_type :

a GType identifying the owner of pspec

g_param_spec_pool_remove ()

void                g_param_spec_pool_remove            (GParamSpecPool *pool,
                                                         GParamSpec *pspec);

Removes a GParamSpec from the pool.

pool :

a GParamSpecPool

pspec :

the GParamSpec to remove

g_param_spec_pool_lookup ()

GParamSpec *        g_param_spec_pool_lookup            (GParamSpecPool *pool,
                                                         const gchar *param_name,
                                                         GType owner_type,
                                                         gboolean walk_ancestors);

Looks up a GParamSpec in the pool.

pool :

a GParamSpecPool

param_name :

the name to look for

owner_type :

the owner to look for

walk_ancestors :

If TRUE, also try to find a GParamSpec with param_name owned by an ancestor of owner_type.

Returns :

The found GParamSpec, or NULL if no matching GParamSpec was found.

g_param_spec_pool_list ()

GParamSpec **       g_param_spec_pool_list              (GParamSpecPool *pool,
                                                         GType owner_type,
                                                         guint *n_pspecs_p);

Gets an array of all GParamSpecs owned by owner_type in the pool.

pool :

a GParamSpecPool

owner_type :

the owner to look for

n_pspecs_p :

return location for the length of the returned array

Returns :

a newly allocated array containing pointers to all GParamSpecs owned by owner_type in the pool

g_param_spec_pool_list_owned ()

GList *             g_param_spec_pool_list_owned        (GParamSpecPool *pool,
                                                         GType owner_type);

Gets an GList of all GParamSpecs owned by owner_type in the pool.

pool :

a GParamSpecPool

owner_type :

the owner to look for

Returns :

a GList of all GParamSpecs owned by owner_type in the poolGParamSpecs.

See Also

g_object_class_install_property(), g_object_set(), g_object_get(), g_object_set_property(), g_object_get_property(), g_value_register_transform_func()