[PATCH v2 3/4] add DUP_ARRAY

From: René Scharfe <l.s.r@web.de>
Date: Jan 1, 2023, 21:14 UTC
Message-ID: <04e99a14-a25b-7e47-8bf3-49442c877c89@web.de>
In-Reply-To: <9bc1bd74-f72c-1b43-df7c-950815babb03@web.de>

Add a macro for allocating and populating a shallow copy of an array. It is intended to replace a sequence like this:

   ALLOC_ARRAY(dst, n);
   COPY_ARRAY(dst, src, n);

With the less repetitve:

   DUP_ARRAY(dst, src, n);

It checks whether the types of source and destination are compatible to ensure the copy can be used safely.

An easier alternative would be to only consider the source and return a void pointer, that could be used like this:

   dst = ARRAY_DUP(src, n);

That would be more versatile, as it could be used in declarations as well. Making it type-safe would require the use of typeof_unqual from C23, though.

So use the safe and compatible variant for now.

Signed-off-by: René Scharfe <l.s.r@web.de>
---
Why typeof_unqual and not just typeof?  To remove const when duplicating
a const array.

 git-compat-util.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/git-compat-util.h b/git-compat-util.h
index e81bb14fc9..44abb240ae 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -1115,6 +1115,11 @@ static inline void move_array(void *dst, const void *src, size_t n, size_t size)
 		memmove(dst, src, st_mult(size, n));
 }

+#define DUP_ARRAY(dst, src, n) do { \
+	size_t dup_array_n_ = (n); \
+	COPY_ARRAY(ALLOC_ARRAY((dst), dup_array_n_), (src), dup_array_n_); \
+} while (0)
+
 /*
  * These functions help you allocate structs with flex arrays, and copy
  * the data directly into the array. For example, if you had:
--
2.39.0