[LLVMdev] Guidance on using pointers vs. references for function arguments

[Chandler Carruth]

On Mon, May 26, 2014 at 4:43 PM, Andrew Trick <atrick at apple.com> wrote:

> This has been discussed before but I can’t find a reference to it. I could
> have sworn this was in the coding convention at some point. Here’s what I
> remember: during early LLVM development there was an effort to establish
> the convention that you described above—use pointer types only when nullptr
> is valid. This led to a lot of redundant declarations and annoying taking
> of addresses and dereferences. It turns out that the convention doesn’t
> really help for most informal/internal APIs. It’s actually no harder to
> debug a SIGSEGV than a nullptr check. I also adhered to this convention in
> a previous project and it never paid off.
>
> Once you begin working on a piece of code you get a feel for which types
> should be passed as pointers and which should be passed as reference. Then
> you try to pass types consistently regardless of whether a null input is
> valid. For example, some types, like the current context, should never be
> copied or passed by value and are obviously not null. That’s lower overhead
> in practice forcing callers to convert to a reference whenever we want to
> skip a null check.
>

FWIW, I disagree.

I much prefer to pass by reference unless there is the expectation of null
inputs. I have never really agreed with the complaints about taking the
address and have never found it to be a burden. I also find the simplicity
of a consistent rule far more appealing than "getting a feel for which
types" should be passed as pointers.

Ironically, using a reference can result in better optimizations by
deleting redundant null checks. While I certainly hope this isn't relevant
to the performance of LLVM, it's still not something to completely
disregard.

Anyways, I've never really seen this become a problem in practice. I'm
pretty happy for folks to use whatever local conventions they want. I'm
usually happy to switch from reference to pointer if I'm hacking some part
of the codebase I don't usually touch and one of the maintainers really
prefers one over the other. It's not a big deal either way.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20140526/eb53ff73/attachment.html>