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/firstboot/firstboot.c b/src/firstboot/firstboot.c
index 308ef9d750..a1f7e226f8 100644
--- a/src/firstboot/firstboot.c
+++ b/src/firstboot/firstboot.c
@@ -575,8 +575,7 @@ static int prompt_root_password(void) {
                         continue;
                 }
 
-                arg_root_password = a;
-                a = NULL;
+                arg_root_password = TAKE_PTR(a);
                 break;
         }