[swift-evolution] [Pitch] Replace 'inout' with '&'

Joe Groff jgroff at apple.com
Mon Dec 21 12:27:13 CST 2015

> On Dec 19, 2015, at 7:12 PM, Dmitri Gribenko via swift-evolution <swift-evolution at swift.org> wrote:
> On Sat, Dec 19, 2015 at 7:06 PM, Jordan Rose via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> -1 to using '&' in the declaration; it's a sigil that doesn't mean anything as is. (I was originally on the side of using 'inout' at the call site as well, i.e. "swap(inout x, inout y)", but it was considered too verbose.)
> I'd actually suggest that we reconsider this.  '&' at the callsite has deep associations with C semantics, and I have too frequently seen buggy code using '&x' combined with one of the C interop implicit conversions to "get a pointer" that the code stores in a variable somewhere.  It is also hard to explain to people that '&x' does not do what they want in that case, "& means address-of, and it returns a pointer here, what do you mean I can't use it?"

Using `inout` at the call site seems reasonable to me. I'd bet the vast majority of `inout` parameters are really the implicit `self` of mutating methods, which already get a pass, so aside from `swap` I wonder how often `&` is in practice.


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