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, 9 insertions, 0 deletions

diff --git a/src/basic/alloc-util.h b/src/basic/alloc-util.h
index ec7808c1f..b1e0edbb7 100644
--- a/src/basic/alloc-util.h
+++ b/src/basic/alloc-util.h
@@ -130,3 +130,12 @@ void* greedy_realloc0(void **p, size_t *allocated, size_t need, size_t size);
                 _new_ = alloca_align(_size_, (align));                  \
                 (void*)memset(_new_, 0, _size_);                        \
         })
+
+/* Takes inspiration from Rusts's Option::take() method: reads and returns a pointer, but at the same time resets it to
+ * NULL. See: https://doc.rust-lang.org/std/option/enum.Option.html#method.take */
+#define TAKE_PTR(ptr)                           \
+        ({                                      \
+                typeof(ptr) _ptr_ = (ptr);      \
+                (ptr) = NULL;                   \
+                _ptr_;                          \
+        })