macro: introduce TAKE_PTR() macro

This macro will read a pointer of any type, return it, and set the
pointer to NULL. This is useful as an explicit concept of passing
ownership of a memory area between pointers.

This takes inspiration from Rust:

https://doc.rust-lang.org/std/option/enum.Option.html#method.take

and was suggested by Alan Jenkins (@sourcejedi).

It drops ~160 lines of code from our codebase, which makes me like it.
Also, I think it clarifies passing of ownership, and thus helps
readability a bit (at least for the initiated who know the new macro)

1 files changed, 1 insertions, 2 deletions

diff --git a/src/libelogind/sd-bus/sd-bus.c b/src/libelogind/sd-bus/sd-bus.c
index eb415e6e3..5df3af5b4 100644
--- a/src/libelogind/sd-bus/sd-bus.c
+++ b/src/libelogind/sd-bus/sd-bus.c
@@ -1350,8 +1350,7 @@ int bus_set_address_user(sd_bus *b) {
         if (asprintf(&s, DEFAULT_USER_BUS_ADDRESS_FMT, ee) < 0)
                 return -ENOMEM;
 
-        b->address = s;
-        s = NULL;
+        b->address = TAKE_PTR(s);
 
         return 0;
 }