In Git's source code, we have this convention that quite a few data structures can be initialized using a macro *_INIT while defining an instance (instead of having to call a function to initialize the data structure). You will see that idiom quite a bit, e.g. `struct strbuf buf = STRBUF_INIT;` This works for oidsets, too: `struct oidset oids = OIDSET_INIT;` is perfectly legal and you can use that data structure right away, without having to call `oidset_init()` first. That pattern is violated by OIDMAP_INIT, though. The first call to oidmap_put() or oidmap_get() will succeed, but by mistake rather than by design: The underlying hashmap is not initialized correctly, as the cmpfn function pointer still points to NULL, but since there are no entries to be compared, cmpfn will not be called. Things break down, though, as soon as there is even one entry. Rather than causing confusion, frustration and needless loss of time due to pointless debugging, let's *rename* OIDMAP_INIT so that developers who have gotten used to the pattern `struct xyz a = XYZ_INIT;` won't do that with oidmaps. An alternative would be to introduce a HASHMAP_INIT(cmp_fn) and use that in oidmap.h. However, there are *no* call sites in Git's source code that would benefit from that macro, i.e. this would be premature optimization (and cost a lot more time than this here trivial patch). Signed-off-by: Johannes Schindelin <johannes.schindelin@xxxxxx> --- Published-As: https://github.com/dscho/git/releases/tag/discourage-OIDMAP_INIT-v1 Fetch-It-Via: git fetch https://github.com/dscho/git discourage-OIDMAP_INIT-v1 oidmap.h | 6 +++++- oidset.h | 7 ++++++- 2 files changed, 11 insertions(+), 2 deletions(-) diff --git a/oidmap.h b/oidmap.h index 18f54cde143..1a73c392b79 100644 --- a/oidmap.h +++ b/oidmap.h @@ -21,7 +21,11 @@ struct oidmap { struct hashmap map; }; -#define OIDMAP_INIT { { NULL } } +/* + * This macro initializes the data structure only incompletely, just enough + * to call oidmap_get() on an empty map. Use oidmap_init() instead. + */ +#define OIDMAP_INIT_INCOMPLETELY { { NULL } } /* * Initializes an oidmap structure. diff --git a/oidset.h b/oidset.h index f4c9e0f9c04..a11d88edc1d 100644 --- a/oidset.h +++ b/oidset.h @@ -22,7 +22,12 @@ struct oidset { struct oidmap map; }; -#define OIDSET_INIT { OIDMAP_INIT } +/* + * It is okay to initialize the map incompletely here because oidset_insert() + * will call oidset_init() (which will call oidmap_init()), and + * oidset_contains() works as intended even before oidset_init() was called. + */ +#define OIDSET_INIT { OIDMAP_INIT_INCOMPLETELY } /** * Returns true iff `set` contains `oid`. base-commit: 936d1b989416a95f593bf81ccae8ac62cd83f279 -- 2.15.1.windows.2
