GParamSpec

GParamSpec — Metadata for parameter specifications

Includes

#include <glib-object.h>

Description

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

Parameter names

A property name consists of one or more segments consisting of ASCII letters and digits, separated by either the - or _ character. The first character of a property name must be a letter. These are the same rules as for signal naming (see g_signal_new()).

When creating and looking up a GParamSpec, either separator can be used, but they cannot be mixed. Using - is considerably more efficient, and is the ‘canonical form’. Using _ is discouraged.

Functions

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.

Parameters

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.

Parameters

pspec

a valid GParamSpec

 

G_IS_PARAM_SPEC()

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

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

Parameters

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.

Parameters

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.

Parameters

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.

Parameters

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 .

Parameters

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 .

Parameters

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.

Parameters

pspec

a valid GParamSpec

 

g_param_spec_ref ()

GParamSpec *
g_param_spec_ref (GParamSpec *pspec);

Increments the reference count of pspec .

[skip]

Parameters

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 .

[skip]

Parameters

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).

Parameters

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.

[skip]

Parameters

pspec

a valid GParamSpec

 

Returns

the GParamSpec that was passed into this function

Since: 2.10


g_param_spec_get_default_value ()

const GValue *
g_param_spec_get_default_value (GParamSpec *pspec);

Gets the default value of pspec as a pointer to a GValue.

The GValue will remain valid for the life of pspec .

Parameters

pspec

a GParamSpec

 

Returns

a pointer to a GValue which must not be modified

Since: 2.38


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 .

Parameters

pspec

a valid GParamSpec

 

value

a GValue of correct type for pspec ; since 2.64, you can also pass an empty GValue, initialized with G_VALUE_INIT

 

g_param_value_defaults ()

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

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

Parameters

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.

Parameters

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().

Parameters

pspec

a valid GParamSpec

 

src_value

source 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.

Parameters

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_is_valid_name ()

gboolean
g_param_spec_is_valid_name (const gchar *name);

Validate a property name for a GParamSpec. This can be useful for dynamically-generated properties which need to be validated at run-time before actually trying to create them.

See canonical parameter names for details of the rules for valid names.

Parameters

name

the canonical name of the property

 

Returns

TRUE if name is a valid property name, FALSE otherwise.

Since: 2.66


g_param_spec_get_name ()

const gchar *
g_param_spec_get_name (GParamSpec *pspec);

Get the name of a GParamSpec.

The name is always an "interned" string (as per g_intern_string()). This allows for pointer-value comparisons.

Parameters

pspec

a valid GParamSpec

 

Returns

the name of pspec .


g_param_spec_get_name_quark ()

GQuark
g_param_spec_get_name_quark (GParamSpec *pspec);

Gets the GQuark for the name.

Parameters

pspec

a GParamSpec

 

Returns

the GQuark for pspec->name .

Since: 2.46


g_param_spec_get_nick ()

const gchar *
g_param_spec_get_nick (GParamSpec *pspec);

Get the nickname of a GParamSpec.

Parameters

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.

Parameters

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().

Parameters

pspec

a valid GParamSpec

 

quark

a GQuark, naming the user data pointer

 

Returns

the user data pointer set, or NULL.

[transfer none]


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.

Parameters

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 .

[skip]

Parameters

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.

Parameters

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.

[transfer none]


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.

Parameters

pspec

a GParamSpec

 

Returns

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

[transfer 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.

See canonical parameter names for details of the rules for name . Names which violate these rules lead to undefined behaviour.

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.

[skip]

Parameters

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.

[type GObject.ParamSpec]


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.

Parameters

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.


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.

Parameters

type_prefixing

Whether the pool will support type-prefixed property names.

 

Returns

a newly allocated GParamSpecPool.

[transfer none]


g_param_spec_pool_insert ()

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

Inserts a GParamSpec in the pool.

Parameters

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.

Parameters

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.

Parameters

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.

[transfer none]


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.

Parameters

pool

a GParamSpecPool

 

owner_type

the owner to look for

 

n_pspecs_p

return location for the length of the returned array.

[out]

Returns

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

[array length=n_pspecs_p][transfer container]


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.

Parameters

pool

a GParamSpecPool

 

owner_type

the owner to look for

 

Returns

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

[transfer container][element-type GObject.ParamSpec]

Types and Values

struct GParamSpec

struct GParamSpec {
  GTypeInstance  g_type_instance;

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

GParamSpec is deprecated and should not be used in newly-written code.

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

Members

GTypeInstance g_type_instance;

private GTypeInstance portion

 

const gchar *name;

name of this parameter: always an interned string

 

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 parameter

 

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().

Members

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_validate().

 

values_cmp ()

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

 

enum GParamFlags

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

Members

G_PARAM_READABLE

the parameter is readable

 

G_PARAM_WRITABLE

the parameter is writable

 

G_PARAM_READWRITE

alias for G_PARAM_READABLE | G_PARAM_WRITABLE

 

G_PARAM_CONSTRUCT

the parameter will be set upon object construction

 

G_PARAM_CONSTRUCT_ONLY

the parameter can 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_EXPLICIT_NOTIFY

calls to g_object_set_property() for this property will not automatically result in a "notify" signal being emitted: the implementation must call g_object_notify() themselves in case the property actually changes. Since: 2.42.

 

G_PARAM_DEPRECATED

the parameter is deprecated and will be removed in a future version. A warning will be generated if it is used while running with G_ENABLE_DIAGNOSTIC=1. Since 2.26

 

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. The maximum allowed is 10.


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().

Members

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_validate().

 

values_cmp ()

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

 

GParamSpecPool

typedef struct _GParamSpecPool GParamSpecPool;

GParamSpecPool is deprecated and should not be used in newly-written code.

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.