Hey,

when declaring a function e. g. like this:

[CCode(simple_generics = true)]
extern GLib.HashTable<K, V> g_hash_table_ref<K, V>(GLib.HashTable<K, V> ht);

The generated C prototype will look like this:
GHashTable* g_hash_table_ref (GType k_type, GBoxedCopyFunc k_dup_func, GDestroyNotify k_destroy_func, GType v_type, GBoxedCopyFunc v_dup_func, GDestroyNotify v_destroy_func, GHashTable* ht);

But because of the simple_generics attribute, at the call site only a single argument (i. e. the hash table) will be passed. The resulting C code can not be compiled due to this.