`in` no longer same as `const ref`

[kinke via Digitalmars-d]

On Monday, 30 January 2017 at 19:05:33 UTC, Q. Schroll wrote:
> Can't we make "in" mean "const scope ref", that binds on 
> r-values, too? Effectively, that's (similar to) what "const T&" 
> in C++ means. It's a non-copying const view on the object. We 
> have the longstanding problem, one must overload a function to 
> effectively bind both l- and r-values. That is what I'd suppose 
> to be the dual to "out".

+1000, I really love this proposal; I *hate* that this point is 
still missing in D in 2017.
It shouldn't even break existing code using `in` (but obviously 
the ABI) just because now a pointer to a const instance is passed 
instead of making a const copy.

Generic stuff:          void foo(in T arg)    // const scope ref 
=> safe `const T&`
By-value optimizations: void foo(const T arg)

I love it.