Re: [Tarantool-patches] [PATCH] Fix wrong make_scoped_guard usage

["Timur Safin" <tsafin@tarantool.org>]

Explicit capture list in lambda - is the correct way, making things clearer!

LGTM

Timur

: -----Original Message-----
: From: Tarantool-patches <tarantool-patches-bounces@dev.tarantool.org> On
: Behalf Of Aleksandr Lyapunov
: Sent: Wednesday, July 8, 2020 3:07 PM
: To: tarantool-patches@dev.tarantool.org
: Subject: [Tarantool-patches] [PATCH] Fix wrong make_scoped_guard usage
: 
: The common pitfall of using a lambda is wrong type of capture -
: by value instead of by reference. The simple example is:
:   struct sequence_def *new_def = NULL;
:   auto def_guard = make_scoped_guard([=] { free(new_def); });
:   // initialize new_def
: The problem is that the lambda captures pointer by value, that
: is NULL and will remain NULL in the lambda while new_def is
: successfully initialized in function scope.
: 
: The patch fixes the problem above and a couple of similar mistakes.
: ---
:  src/box/alter.cc | 4 ++--
:  src/main.cc      | 2 +-
:  2 files changed, 3 insertions(+), 3 deletions(-)
: 
: diff --git a/src/box/alter.cc b/src/box/alter.cc
: index bb42548..3109fb4 100644
: --- a/src/box/alter.cc
: +++ b/src/box/alter.cc
: @@ -3560,7 +3560,7 @@ on_replace_dd_func(struct trigger * /* trigger */,
: void *event)
:  		 * definition to support upgrade script.
:  		 */
:  		struct func_def *old_def = NULL, *new_def = NULL;
: -		auto guard = make_scoped_guard([=] {
: +		auto guard = make_scoped_guard([&old_def, &new_def] {
:  			free(old_def);
:  			free(new_def);
:  		});
: @@ -4431,7 +4431,7 @@ on_replace_dd_sequence(struct trigger * /* trigger
: */, void *event)
:  	struct tuple *new_tuple = stmt->new_tuple;
: 
:  	struct sequence_def *new_def = NULL;
: -	auto def_guard = make_scoped_guard([=] { free(new_def); });
: +	auto def_guard = make_scoped_guard([&new_def] { free(new_def); });
: 
:  	struct sequence *seq;
:  	if (old_tuple == NULL && new_tuple != NULL) {		/* INSERT */
: diff --git a/src/main.cc b/src/main.cc
: index 2c96391..e622042 100644
: --- a/src/main.cc
: +++ b/src/main.cc
: @@ -729,7 +729,7 @@ main(int argc, char **argv)
:  	/* Lua interpeter options, e.g. -e and -l */
:  	int optc = 0;
:  	const char **optv = NULL;
: -	auto guard = make_scoped_guard([=]{ if (optc) free(optv); });
: +	auto guard = make_scoped_guard([&optc, &optv]{ if (optc) free(optv);
: });
: 
:  	static struct option longopts[] = {
:  		{"help", no_argument, 0, 'h'},
: --
: 2.7.4