gparamspec.sgml

This GLib version 2.16.1. GLib is the low-level core library that forms the basis for projects such

<!-- ##### SECTION Title ##### -->
GParamSpec

<!-- ##### SECTION Short_Description ##### -->
Metadata for parameter specifications

<!-- ##### SECTION Long_Description ##### -->
<para>
#GParamSpec is an object structure that encapsulates the metadata
required to specify parameters, such as e.g. #GObject properties.
</para>
<para id="canonical-parameter-name">
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.
</para>

<!-- ##### SECTION See_Also ##### -->
<para>
g_object_class_install_property(), g_object_set(), g_object_get(),
g_object_set_property(), g_object_get_property(), g_value_register_transform_func()
</para>

<!-- ##### SECTION Stability_Level ##### -->


<!-- ##### MACRO G_TYPE_IS_PARAM ##### -->
<para>
Returns whether @type "is a" %G_TYPE_PARAM.
</para>

@type: a #GType ID


<!-- ##### MACRO G_PARAM_SPEC ##### -->
<para>
Casts a derived #GParamSpec object (e.g. of type #GParamSpecInt) into
a #GParamSpec object.
</para>

@pspec: a valid #GParamSpec


<!-- ##### MACRO G_IS_PARAM_SPEC ##### -->
<para>
Checks whether @pspec "is a" valid #GParamSpec structure of type %G_TYPE_PARAM
or derived.
</para>

@pspec: a #GParamSpec


<!-- ##### MACRO G_PARAM_SPEC_CLASS ##### -->
<para>
Casts a derived #GParamSpecClass structure into a #GParamSpecClass structure.
</para>

@pclass: a valid #GParamSpecClass


<!-- ##### MACRO G_IS_PARAM_SPEC_CLASS ##### -->
<para>
Checks whether @pclass "is a" valid #GParamSpecClass structure of type 
%G_TYPE_PARAM or derived.
</para>

@pclass: a #GParamSpecClass


<!-- ##### MACRO G_PARAM_SPEC_GET_CLASS ##### -->
<para>
Retrieves the #GParamSpecClass of a #GParamSpec.
</para>

@pspec: a valid #GParamSpec


<!-- ##### MACRO G_PARAM_SPEC_TYPE ##### -->
<para>
Retrieves the #GType of this @pspec.
</para>

@pspec: a valid #GParamSpec


<!-- ##### MACRO G_PARAM_SPEC_TYPE_NAME ##### -->
<para>
Retrieves the #GType name of this @pspec.
</para>

@pspec: a valid #GParamSpec


<!-- ##### MACRO G_PARAM_SPEC_VALUE_TYPE ##### -->
<para>
Retrieves the #GType to initialize a #GValue for this parameter.
</para>

@pspec: a valid #GParamSpec


<!-- ##### STRUCT GParamSpec ##### -->
<para>
All fields of the <structname>GParamSpec</structname> struct are private and
should not be used directly, except for the following:
</para>

@g_type_instance: private #GTypeInstance portion
@name:            name of this parameter
@flags:           #GParamFlags flags for this parameter
@value_type:      the #GValue type for this parameter
@owner_type:      #GType type that uses (introduces) this paremeter

<!-- ##### STRUCT GParamSpecClass ##### -->
<para>
The class structure for the <structname>GParamSpec</structname> type.
Normally, <structname>GParamSpec</structname> classes are filled by
g_param_type_register_static().
</para>

@g_type_class: the parent class
@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 ##### -->
<para>
Through the #GParamFlags flag values, certain aspects of parameters
can be configured.
</para>

@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: 
@G_PARAM_STATIC_NICK: 
@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

<!-- ##### MACRO G_PARAM_READWRITE ##### -->
<para>
#GParamFlags value alias for %G_PARAM_READABLE | %G_PARAM_WRITABLE.
</para>



<!-- ##### MACRO G_PARAM_STATIC_STRINGS ##### -->
<para>
#GParamFlags value alias for %G_PARAM_STATIC_NAME | %G_PARAM_STATIC_NICK | %G_PARAM_STATIC_BLURB.

Since 2.13.0
</para>



<!-- ##### MACRO G_PARAM_MASK ##### -->
<para>
Mask containing the bits of #GParamSpec.flags which are reserved for GLib.
</para>



<!-- ##### MACRO G_PARAM_USER_SHIFT ##### -->
<para>
Minimum shift count to be used for user defined flags, to be stored in
#GParamSpec.flags.
</para>



<!-- ##### FUNCTION g_param_spec_ref ##### -->
<para>
Increments the reference count of @pspec.
</para>

@pspec:   a valid #GParamSpec
@Returns: the #GParamSpec that was passed into this function


<!-- ##### FUNCTION g_param_spec_unref ##### -->
<para>
Decrements the reference count of a @pspec.
</para>

@pspec: a valid #GParamSpec


<!-- ##### FUNCTION g_param_spec_sink ##### -->
<para>
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 
<literal>g_param_spec_ref (pspec); g_param_spec_sink (pspec);</literal>
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).
</para>

@pspec: a valid #GParamSpec


<!-- ##### FUNCTION g_param_spec_ref_sink ##### -->
<para>
Convenience function to ref and sink a #GParamSpec.
</para>

@pspec: a valid #GParamSpec
@Returns: the #GParamSpec that was passed into this function
@Since: 2.10


<!-- ##### FUNCTION g_param_value_set_default ##### -->
<para>
Sets @value to its default value as specified in @pspec.
</para>

@pspec: a valid #GParamSpec
@value: a #GValue of correct type for @pspec


<!-- ##### FUNCTION g_param_value_defaults ##### -->
<para>
Checks whether @value contains the default value as specified in @pspec.
</para>

@pspec:   a valid #GParamSpec
@value:   a #GValue of correct type for @pspec
@Returns: whether @value contains the canonical default for this @pspec


<!-- ##### FUNCTION g_param_value_validate ##### -->
<para>
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.
</para>

@pspec:   a valid #GParamSpec
@value:   a #GValue of correct type for @pspec
@Returns: whether modifying @value was necessary to ensure validity


<!-- ##### FUNCTION g_param_value_convert ##### -->
<para>
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