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/udev/udev-builtin-path_id.c b/src/udev/udev-builtin-path_id.c
index 0a32363deb..7d967e04de 100644
--- a/src/udev/udev-builtin-path_id.c
+++ b/src/udev/udev-builtin-path_id.c
@@ -62,10 +62,8 @@ static void path_prepend(char **path, const char *fmt, ...) {
                 }
 
                 free_and_replace(*path, new);
-        } else {
-                *path = pre;
-                pre = NULL;
-        }
+        } else
+                *path = TAKE_PTR(pre);
 }
 
 /*