VariantDict is a mutable interface to GVariant dictionaries.

It can be used for doing a sequence of dictionary lookups in an efficient way on an existing GVariant 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 variantDictClear.

Heap-allocated VariantDict follows normal refcounting rules: you allocate it with variantDictNew and use variantDictRef and variantDictUnref.

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

Using a stack-allocated GVariantDict

C code

 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

C code

 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;
 }

Since: 2.40