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OFFSETOF_VAR macro to simplify hashmap iterators

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While we cannot rely on a `__typeof__' operator being portable
to use with `offsetof'; we can calculate the pointer offset
using an existing pointer and the address of a member using
pointer arithmetic for compilers without `__typeof__'.

This allows us to simplify usage of hashmap iterator macros
by not having to specify a type when a pointer of that type
is already given.

In the future, list iterator macros (e.g. list_for_each_entry)
may also be implemented using OFFSETOF_VAR to save hackers the
trouble of using container_of/list_entry macros and without
relying on non-portable `__typeof__'.

v3: use `__typeof__' to avoid clang warnings

Signed-off-by: Eric Wong <e@80x24.org>
Reviewed-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Eric Wong
2019-10-06 23:30:41 +00:00
committed by Junio C Hamano
parent c8e424c9c9
commit 23dee69f53
15 changed files with 56 additions and 45 deletions
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4
builtin/difftool.c
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@ -539,7 +539,7 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
* change in the recorded SHA1 for the submodule.
*/
hashmap_for_each_entry(&submodules, &iter, entry,
struct pair_entry, entry /* member name */) {
entry /* member name */) {
if (*entry->left) {
add_path(&ldir, ldir_len, entry->path);
ensure_leading_directories(ldir.buf);
@ -558,7 +558,7 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
* This loop replicates that behavior.
*/
hashmap_for_each_entry(&symlinks2, &iter, entry,
struct pair_entry, entry /* member name */) {
entry /* member name */) {
if (*entry->left) {
add_path(&ldir, ldir_len, entry->path);
ensure_leading_directories(ldir.buf);