glib/gobject/gvalue.c

/* GObject - GLib Type, Object, Parameter and Signal Library
 * Copyright (C) 1997-1999, 2000-2001 Tim Janik and Red Hat, Inc.
 *
 * SPDX-License-Identifier: LGPL-2.1-or-later
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General
 * Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
 */

/*
 * FIXME: MT-safety
 */

#include "config.h"

#include <string.h>

#include "gvalue.h"
#include "gvaluecollector.h"
#include "gbsearcharray.h"
#include "gtype-private.h"


/* --- typedefs & structures --- */
typedef struct {
  GType src_type;
  GType dest_type;
  GValueTransform func;
} TransformEntry;


/* --- prototypes --- */
static gint	transform_entries_cmp	(gconstpointer bsearch_node1,
					 gconstpointer bsearch_node2);


/* --- variables --- */
static GBSearchArray *transform_array = NULL;
static GBSearchConfig transform_bconfig = {
  sizeof (TransformEntry),
  transform_entries_cmp,
  G_BSEARCH_ARRAY_ALIGN_POWER2,
};


/* --- functions --- */
void
_g_value_c_init (void)
{
  transform_array = g_bsearch_array_create (&transform_bconfig);
}

static inline void		/* keep this function in sync with gvaluecollector.h and gboxed.c */
value_meminit (GValue *value,
	       GType   value_type)
{
  value->g_type = value_type;
  memset (value->data, 0, sizeof (value->data));
}

/**
 * g_value_init:
 * @value: a zero-filled (cleared) [struct@GObject.Value] structure
 * @g_type: type the [struct@GObject.Value] should hold values of
 *
 * Initializes @value to store values of the given @type, and sets its value
 * to the initial value for @type.
 *
 * This must be called before any other methods on a [struct@GObject.Value], so
 * the value knows what type it’s meant to store.
 *
 * ```c
 *   GValue value = G_VALUE_INIT;
 *
 *   g_value_init (&value, SOME_G_TYPE);
 *   …
 *   g_value_unset (&value);
 * ```
 *
 * Returns: (transfer none): the [struct@GObject.Value] structure that has been
 *   passed in
 */
GValue*
g_value_init (GValue *value,
	      GType   g_type)
{
  GTypeValueTable *value_table;
  /* g_return_val_if_fail (G_TYPE_IS_VALUE (g_type), NULL);	be more elaborate below */
  g_return_val_if_fail (value != NULL, NULL);
  /* g_return_val_if_fail (G_VALUE_TYPE (value) == 0, NULL);	be more elaborate below */

  value_table = g_type_value_table_peek (g_type);

  if (value_table && G_VALUE_TYPE (value) == 0)
    {
      /* setup and init */
      value_meminit (value, g_type);
      value_table->value_init (value);
    }
  else if (G_VALUE_TYPE (value))
    g_critical ("%s: cannot initialize GValue with type '%s', the value has already been initialized as '%s'",
	        G_STRLOC,
	        g_type_name (g_type),
	        g_type_name (G_VALUE_TYPE (value)));
  else /* !G_TYPE_IS_VALUE (g_type) */
    g_critical ("%s: cannot initialize GValue with type '%s', %s",
                G_STRLOC,
                g_type_name (g_type),
                value_table ? "this type is abstract with regards to GValue use, use a more specific (derived) type" : "this type has no GTypeValueTable implementation");
  return value;
}

/**
 * g_value_copy:
 * @src_value: an initialized [struct@GObject.Value] structure
 * @dest_value: an initialized [struct@GObject.Value] structure of the same type
 *   as @src_value
 *
 * Copies the value of @src_value into @dest_value.
 */
void
g_value_copy (const GValue *src_value,
	      GValue       *dest_value)
{
  g_return_if_fail (src_value);
  g_return_if_fail (dest_value);
  g_return_if_fail (g_value_type_compatible (G_VALUE_TYPE (src_value), G_VALUE_TYPE (dest_value)));
  
  if (src_value != dest_value)
    {
      GType dest_type = G_VALUE_TYPE (dest_value);
      GTypeValueTable *value_table = g_type_value_table_peek (dest_type);

      g_return_if_fail (value_table);

      /* make sure dest_value's value is free()d */
      if (value_table->value_free)
	value_table->value_free (dest_value);

      /* setup and copy */
      value_meminit (dest_value, dest_type);
      value_table->value_copy (src_value, dest_value);
    }
}

/**
 * g_value_reset:
 * @value: an initialized [struct@GObject.Value] structure
 *
 * Clears the current value in @value and resets it to the initial value
 * (as if the value had just been initialized using
 * [method@GObject.Value.init]).
 *
 * Returns: (transfer none): the [struct@GObject.Value] structure that has been passed in
 */
GValue*
g_value_reset (GValue *value)
{
  GTypeValueTable *value_table;
  GType g_type;

  g_return_val_if_fail (value, NULL);
  g_type = G_VALUE_TYPE (value);

  value_table = g_type_value_table_peek (g_type);
  g_return_val_if_fail (value_table, NULL);

  /* make sure value's value is free()d */
  if (value_table->value_free)
    value_table->value_free (value);

  /* setup and init */
  value_meminit (value, g_type);
  value_table->value_init (value);

  return value;
}

/**
 * g_value_unset:
 * @value: an initialized [struct@GObject.Value] structure
 *
 * Clears the current value in @value (if any) and ‘unsets’ the type.
 *
 * This releases all resources associated with this [struct@GObject.Value]. An
 * unset value is the same as a cleared (zero-filled)
 * [struct@GObject.Value] structure set to `G_VALUE_INIT`.
 */
void
g_value_unset (GValue *value)
{
  GTypeValueTable *value_table;
  
  if (value->g_type == 0)
    return;

  g_return_if_fail (value);

  value_table = g_type_value_table_peek (G_VALUE_TYPE (value));
  g_return_if_fail (value_table);

  if (value_table->value_free)
    value_table->value_free (value);
  memset (value, 0, sizeof (*value));
}

/**
 * g_value_fits_pointer:
 * @value: an initialized [struct@GObject.Value] structure
 *
 * Determines if @value will fit inside the size of a pointer value.
 *
 * This is an internal function introduced mainly for C marshallers.
 *
 * Returns: true if @value will fit inside a pointer value; false otherwise
 */
gboolean
g_value_fits_pointer (const GValue *value)
{
  GTypeValueTable *value_table;

  g_return_val_if_fail (value, FALSE);

  value_table = g_type_value_table_peek (G_VALUE_TYPE (value));
  g_return_val_if_fail (value_table, FALSE);

  return value_table->value_peek_pointer != NULL;
}

/**
 * g_value_peek_pointer:
 * @value: an initialized [struct@GObject.Value] structure
 *
 * Returns the value contents as a pointer.
 *
 * This function asserts that [method@GObject.Value.fits_pointer] returned true
 * for the passed in value.
 *
 * This is an internal function introduced mainly for C marshallers.
 *
 * Returns: (transfer none): the value contents as a pointer
 */
gpointer
g_value_peek_pointer (const GValue *value)
{
  GTypeValueTable *value_table;

  g_return_val_if_fail (value, NULL);

  value_table = g_type_value_table_peek (G_VALUE_TYPE (value));
  g_return_val_if_fail (value_table, NULL);

  if (!value_table->value_peek_pointer)
    {
      g_return_val_if_fail (g_value_fits_pointer (value) == TRUE, NULL);
      return NULL;
    }

  return value_table->value_peek_pointer (value);
}

/**
 * g_value_set_instance:
 * @value: an initialized [struct@GObject.Value] structure
 * @instance: (nullable): the instance
 *
 * Sets @value from an instantiatable type.
 *
 * This calls the [callback@GObject.TypeValueCollectFunc] function for the type
 * the [struct@GObject.Value] contains.
 */
void
g_value_set_instance (GValue  *value,
		      gpointer instance)
{
  GType g_type;
  GTypeValueTable *value_table;
  GTypeCValue cvalue;
  gchar *error_msg;

  g_return_if_fail (value);
  g_type = G_VALUE_TYPE (value);
  value_table = g_type_value_table_peek (g_type);
  g_return_if_fail (value_table);

  if (instance)
    {
      g_return_if_fail (G_TYPE_CHECK_INSTANCE (instance));
      g_return_if_fail (g_value_type_compatible (G_TYPE_FROM_INSTANCE (instance), G_VALUE_TYPE (value)));
    }
  
  g_return_if_fail (strcmp (value_table->collect_format, "p") == 0);
  
  memset (&cvalue, 0, sizeof (cvalue));
  cvalue.v_pointer = instance;
  
  /* make sure value's value is free()d */
  if (value_table->value_free)
    value_table->value_free (value);

  /* setup and collect */
  value_meminit (value, g_type);
  error_msg = value_table->collect_value (value, 1, &cvalue, 0);
  if (error_msg)
    {
      g_critical ("%s: %s", G_STRLOC, error_msg);
      g_free (error_msg);
      
      /* we purposely leak the value here, it might not be
       * in a correct state if an error condition occurred
       */
      value_meminit (value, g_type);
      value_table->value_init (value);
    }
}

/**
 * g_value_init_from_instance:
 * @value: a zero-filled (cleared) [struct@GObject.Value] structure
 * @instance: (type GObject.TypeInstance): the instance
 *
 * Initializes and sets @value from an instantiatable type.
 *
 * This calls the [callback@GObject.TypeValueCollectFunc] function for the type
 * the [struct@GObject.Value] contains.
 *
 * Note: The @value will be initialised with the exact type of
 * @instance.  If you wish to set the @value’s type to a different
 * [type@GObject.Type] (such as a parent class type), you need to manually call
 * [method@GObject.Value.init] and [method@GObject.Value.set_instance].
 *
 * Since: 2.42
 */
void
g_value_init_from_instance (GValue  *value,
                            gpointer instance)
{
  g_return_if_fail (value != NULL && G_VALUE_TYPE(value) == 0);

  if (G_IS_OBJECT (instance))
    {
      /* Fast-path.
       * If G_IS_OBJECT() succeeds we know:
       * * that instance is present and valid
       * * that it is a GObject, and therefore we can directly
       *   use the collect implementation (g_object_ref) */
      value_meminit (value, G_TYPE_FROM_INSTANCE (instance));
      value->data[0].v_pointer = g_object_ref (instance);
    }
  else
    {  
      GType g_type;
      GTypeValueTable *value_table;
      GTypeCValue cvalue;
      gchar *error_msg;

      g_return_if_fail (G_TYPE_CHECK_INSTANCE (instance));

      g_type = G_TYPE_FROM_INSTANCE (instance);
      value_table = g_type_value_table_peek (g_type);
      g_return_if_fail (strcmp (value_table->collect_format, "p") == 0);

      memset (&cvalue, 0, sizeof (cvalue));
      cvalue.v_pointer = instance;

      /* setup and collect */
      value_meminit (value, g_type);
      value_table->value_init (value);
      error_msg = value_table->collect_value (value, 1, &cvalue, 0);
      if (error_msg)
        {
          g_critical ("%s: %s", G_STRLOC, error_msg);
          g_free (error_msg);

          /* we purposely leak the value here, it might not be
           * in a correct state if an error condition occurred
           */
          value_meminit (value, g_type);
          value_table->value_init (value);
        }
    }
}

static GType
transform_lookup_get_parent_type (GType type)
{
  if (g_type_fundamental (type) == G_TYPE_INTERFACE)
    return g_type_interface_instantiatable_prerequisite (type);

  return g_type_parent (type);
}

static GValueTransform
transform_func_lookup (GType src_type,
		       GType dest_type)
{
  TransformEntry entry;

  entry.src_type = src_type;
  do
    {
      entry.dest_type = dest_type;
      do
	{
	  TransformEntry *e;
	  
	  e = g_bsearch_array_lookup (transform_array, &transform_bconfig, &entry);
	  if (e)
	    {
	      /* need to check that there hasn't been a change in value handling */
	      if (g_type_value_table_peek (entry.dest_type) == g_type_value_table_peek (dest_type) &&
		  g_type_value_table_peek (entry.src_type) == g_type_value_table_peek (src_type))
		return e->func;
	    }
	  entry.dest_type = transform_lookup_get_parent_type (entry.dest_type);
	}
      while (entry.dest_type);
      
      entry.src_type = transform_lookup_get_parent_type (entry.src_type);
    }
  while (entry.src_type);

  return NULL;
}

static gint
transform_entries_cmp (gconstpointer bsearch_node1,
		       gconstpointer bsearch_node2)
{
  const TransformEntry *e1 = bsearch_node1;
  const TransformEntry *e2 = bsearch_node2;
  gint cmp = G_BSEARCH_ARRAY_CMP (e1->src_type, e2->src_type);

  if (cmp)
    return cmp;
  else
    return G_BSEARCH_ARRAY_CMP (e1->dest_type, e2->dest_type);
}

/**
 * g_value_register_transform_func: (skip)
 * @src_type: source type
 * @dest_type: target type
 * @transform_func: a function which transforms values of type @src_type
 *   into values of type @dest_type
 *
 * Registers a value transformation function for use in
 * [method@GObject.Value.transform].
 *
 * Any previously registered transformation function for @src_type and
 * @dest_type will be replaced.
 */
void
g_value_register_transform_func (GType           src_type,
				 GType           dest_type,
				 GValueTransform transform_func)
{
  TransformEntry entry;

  /* these checks won't pass for dynamic types.
   * g_return_if_fail (G_TYPE_HAS_VALUE_TABLE (src_type));
   * g_return_if_fail (G_TYPE_HAS_VALUE_TABLE (dest_type));
   */
  g_return_if_fail (transform_func != NULL);

  entry.src_type = src_type;
  entry.dest_type = dest_type;

#if 0 /* let transform function replacement be a valid operation */
  if (g_bsearch_array_lookup (transform_array, &transform_bconfig, &entry))
    g_warning ("reregistering value transformation function (%p) for '%s' to '%s'",
	       transform_func,
	       g_type_name (src_type),
	       g_type_name (dest_type));
#endif

  entry.func = transform_func;
  transform_array = g_bsearch_array_replace (transform_array, &transform_bconfig, &entry);
}

/**
 * g_value_type_transformable:
 * @src_type: source type
 * @dest_type: target type
 *
 * Checks whether [method@GObject.Value.transform] is able to transform values
 * of type @src_type into values of type @dest_type.
 *
 * Note that for the types to be transformable, they must be compatible or a
 * transformation function must be registered using
 * [func@GObject.Value.register_transform_func].
 *
 * Returns: true if the transformation is possible; false otherwise
 */
gboolean
g_value_type_transformable (GType src_type,
			    GType dest_type)
{
  g_return_val_if_fail (src_type, FALSE);
  g_return_val_if_fail (dest_type, FALSE);

  return (g_value_type_compatible (src_type, dest_type) ||
	  transform_func_lookup (src_type, dest_type) != NULL);
}

/**
 * g_value_type_compatible:
 * @src_type: source type to be copied
 * @dest_type: destination type for copying
 *
 * Checks whether a [method@GObject.Value.copy] is able to copy values of type
 * @src_type into values of type @dest_type.
 *
 * Returns: true if the copy is possible; false otherwise
 */
gboolean
g_value_type_compatible (GType src_type,
			 GType dest_type)
{
  g_return_val_if_fail (src_type, FALSE);
  g_return_val_if_fail (dest_type, FALSE);

  /* Fast path */
  if (src_type == dest_type)
    return TRUE;

  return (g_type_is_a (src_type, dest_type) &&
	  g_type_value_table_peek (dest_type) == g_type_value_table_peek (src_type));
}

/**
 * g_value_transform:
 * @src_value: source value
 * @dest_value: target value
 *
 * Tries to cast the contents of @src_value into a type appropriate
 * to store in @dest_value.
 *
 * If a transformation is not possible, @dest_value is not modified.
 *
 * For example, this could transform a `G_TYPE_INT` value into a `G_TYPE_FLOAT`
 * value.
 *
 * Performing transformations between value types might incur precision loss.
 * Especially transformations into strings might reveal seemingly arbitrary
 * results and the format of particular transformations to strings is not
 * guaranteed over time.
 *
 * Returns: true on success; false otherwise
 */
gboolean
g_value_transform (const GValue *src_value,
		   GValue       *dest_value)
{
  GType dest_type;

  g_return_val_if_fail (src_value, FALSE);
  g_return_val_if_fail (dest_value, FALSE);

  dest_type = G_VALUE_TYPE (dest_value);
  if (g_value_type_compatible (G_VALUE_TYPE (src_value), dest_type))
    {
      g_value_copy (src_value, dest_value);
      
      return TRUE;
    }
  else
    {
      GValueTransform transform = transform_func_lookup (G_VALUE_TYPE (src_value), dest_type);

      if (transform)
	{
	  g_value_unset (dest_value);
	  
	  /* setup and transform */
	  value_meminit (dest_value, dest_type);
	  transform (src_value, dest_value);
	  
	  return TRUE;
	}
    }
  return FALSE;
}