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/vconsole/vconsole-setup.c b/src/vconsole/vconsole-setup.c
index a9cc2bf63c..6bde3da1c8 100644
--- a/src/vconsole/vconsole-setup.c
+++ b/src/vconsole/vconsole-setup.c
@@ -358,8 +358,7 @@ static int find_source_vc(char **ret_path, unsigned *ret_idx) {
 
                 /* all checks passed, return this one as a source console */
                 *ret_idx = i;
-                *ret_path = path;
-                path = NULL;
+                *ret_path = TAKE_PTR(path);
                 ret_fd = fd;
                 fd = -1;
                 return ret_fd;