VariantDict

VariantDict is a mutable interface to Variant dictionaries.

It can be used for doing a sequence of dictionary lookups in an efficient way on an existing Variant dictionary or it can be used to construct new dictionaries with a hashtable-like interface. It can also be used for taking existing dictionaries and modifying them in order to create new ones.

VariantDict can only be used with g_variant_type_vardict dictionaries.

It is possible to use VariantDict allocated on the stack or on the heap. When using a stack-allocated VariantDict, you begin with a call to g_variant_dict_init and free the resources with a call to clear.

Heap-allocated VariantDict follows normal refcounting rules: you allocate it with VariantDict and use g_variant_dict_ref and g_variant_dict_unref.

end is used to convert the VariantDict back into a dictionary-type Variant. When used with stack-allocated instances, this also implicitly frees all associated memory, but for heap-allocated instances, you must still call g_variant_dict_unref afterwards.

You will typically want to use a heap-allocated VariantDict when you expose it as part of an API. For most other uses, the stack-allocated form will be more convenient.

Consider the following two examples that do the same thing in each style: take an existing dictionary and look up the "count" uint32 key, adding 1 to it if it is found, or returning an error if the key is not found. Each returns the new dictionary as a floating Variant.

Using a stack-allocated GVariantDict

  GVariant *
  add_to_count (GVariant  *orig,
                GError   **error)
  {
    GVariantDict dict;
    guint32 count;

    g_variant_dict_init (&dict, orig);
    if (!g_variant_dict_lookup (&dict, "count", "u", &count))
      {
        g_set_error (...);
        g_variant_dict_clear (&dict);
        return NULL;
      }

    g_variant_dict_insert (&dict, "count", "u", count + 1);

    return g_variant_dict_end (&dict);
  }

Using heap-allocated GVariantDict

  GVariant *
  add_to_count (GVariant  *orig,
                GError   **error)
  {
    GVariantDict *dict;
    GVariant *result;
    guint32 count;

    dict = g_variant_dict_new (orig);

    if (g_variant_dict_lookup (dict, "count", "u", &count))
      {
        g_variant_dict_insert (dict, "count", "u", count + 1);
        result = g_variant_dict_end (dict);
      }
    else
      {
        g_set_error (...);
        result = NULL;
      }

    g_variant_dict_unref (dict);

    return result;
  }