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ghash: Add g_hash_table_new_similar()

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This function creates a new hash table, but inherits the functions used
for the hash, comparison, and key/value memory management functions from
another hash table.

The primary use case is to implement a behaviour where you maintain a
hash table by regenerating it, letting the values not migrated be freed.
See the following pseudo code:

```
GHashTable *ht;

init(GList *resources) {
  ht = g_hash_table_new (g_str_hash, g_str_equal, g_free, g_free);
  for (r in resources)
    g_hash_table_insert (ht, strdup (resource_get_key (r)), create_value (r));
}

update(GList *resources) {
  GHashTable *new_ht = g_hash_table_new_similar (ht);

  for (r in resources) {
    if (g_hash_table_steal_extended (ht, resource_get_key (r), &key, &value))
      g_hash_table_insert (new_ht, key, value);
    else
      g_hash_table_insert (new_ht, strdup (resource_get_key (r)), create_value (r));
  }
  g_hash_table_unref (ht);
  ht = new_ht;
}
```
This commit is contained in:
Jonas Ådahl
2021-12-23 00:58:54 +01:00
parent 41d80f5029
commit 283d9e0c15
4 changed files with 74 additions and 0 deletions
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44
glib/tests/hash.c
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@@ -1345,6 +1345,49 @@ test_lookup_extended (void)
g_hash_table_unref (hash);
}
static void
inc_state (gpointer user_data)
{
int *state = user_data;
g_assert_cmpint (*state, ==, 0);
*state = 1;
}
static void
test_new_similar (void)
{
GHashTable *hash1;
GHashTable *hash2;
int state1;
int state2;
hash1 = g_hash_table_new_full (g_str_hash, g_str_equal,
g_free, inc_state);
state1 = 0;
g_hash_table_insert (hash1,
g_strdup ("test"),
&state1);
g_assert_true (g_hash_table_lookup (hash1, "test") == &state1);
hash2 = g_hash_table_new_similar (hash1);
g_assert_true (g_hash_table_lookup (hash1, "test") == &state1);
g_assert_null (g_hash_table_lookup (hash2, "test"));
state2 = 0;
g_hash_table_insert (hash2, g_strdup ("test"), &state2);
g_assert_true (g_hash_table_lookup (hash2, "test") == &state2);
g_hash_table_remove (hash2, "test");
g_assert_cmpint (state2, ==, 1);
g_assert_cmpint (state1, ==, 0);
g_hash_table_remove (hash1, "test");
g_assert_cmpint (state1, ==, 1);
g_hash_table_unref (hash1);
g_hash_table_unref (hash2);
}
struct _GHashTable
{
gsize size;
@@ -1685,6 +1728,7 @@ main (int argc, char *argv[])
g_test_add_func ("/hash/steal-extended", test_steal_extended);
g_test_add_func ("/hash/steal-extended/optional", test_steal_extended_optional);
g_test_add_func ("/hash/lookup-extended", test_lookup_extended);
g_test_add_func ("/hash/new-similar", test_new_similar);
/* tests for individual bugs */
g_test_add_func ("/hash/lookup-null-key", test_lookup_null_key);