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/shared/dns-domain.c b/src/shared/dns-domain.c
index 8c807e0e23..89d18431e4 100644
--- a/src/shared/dns-domain.c
+++ b/src/shared/dns-domain.c
@@ -295,8 +295,7 @@ int dns_label_escape_new(const char *p, size_t l, char **ret) {
         if (r < 0)
                 return r;
 
-        *ret = s;
-        s = NULL;
+        *ret = TAKE_PTR(s);
 
         return r;
 }
@@ -601,8 +600,7 @@ int dns_name_endswith(const char *name, const char *suffix) {
 
                         /* Not the same, let's jump back, and try with the next label again */
                         s = suffix;
-                        n = saved_n;
-                        saved_n = NULL;
+                        n = TAKE_PTR(saved_n);
                 }
         }
 }