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, 2 insertions, 4 deletions

diff --git a/src/resolve/resolved-link-bus.c b/src/resolve/resolved-link-bus.c
index 82a29289d..7e7308a81 100644
--- a/src/resolve/resolved-link-bus.c
+++ b/src/resolve/resolved-link-bus.c
@@ -496,8 +496,7 @@ int bus_link_method_set_dnssec_negative_trust_anchors(sd_bus_message *message, v
         }
 
         set_free_free(l->dnssec_negative_trust_anchors);
-        l->dnssec_negative_trust_anchors = ns;
-        ns = NULL;
+        l->dnssec_negative_trust_anchors = TAKE_PTR(ns);
 
         (void) link_save_user(l);
 
@@ -621,8 +620,7 @@ int link_node_enumerator(sd_bus *bus, const char *path, void *userdata, char ***
         }
 
         l[c] = NULL;
-        *nodes = l;
-        l = NULL;
+        *nodes = TAKE_PTR(l);
 
         return 1;
 }