On 24.03.2018 15:56, kinke wrote:
On Saturday, 24 March 2018 at 13:49:13 UTC, Timon Gehr wrote:
What I'm saying is that I don't really buy Jonathan's argument.
Basically, you should just pass the correct arguments to functions, as
you always need to do. If you cannot use the result of some mutation
that you need to use, you will probably notice.
I agree, but restricting it to const ref would be enough for almost all
of my use cases. The MS C++ compiler just emits a warning when binding
an rvalue to a mutable ref ('nonstandard extension used'), I'd find that
absolutely viable for D too.
...
A warning is not viable. (There's no good way to fix it.)
There are only three sensible ways to fix the problem:
1. Just allow rvalue arguments to bind to ref parameters. (My
preferred solution, though it will make the overloading rules slightly
more complicated.)
I always thought the main concern was potential escaping refs to the
rvalue, which would be solvable by allowing rvalues to be bound to
`scope ref` params only. That'd be my preferred choice as well.
...
There is no difference between escaping refs to an rvalue and escaping
refs to a short-lived lvalue, as the callee has no idea where the
address is coming from anyway. According to Walter, ref parameters are
not supposed to be escaped, and @safe will enforce it.
Also, AFAIU, "scope" in "scope ref T" already applies to "T", not "ref".
2. Add some _new_ annotation for ref parameters that signifies that
you want the same treatment for them that the implicit 'this'
reference gets. (A close second.)
*Shudder*.
...
Well, it beats "const".
3. Continue to require code bloat (auto ref) or manual boilerplate
(overloads). (I'm not very fond of this option, but it does not
require a language change.)
While `auto ref` seems to have worked out surprisingly well for code
written in D, it doesn't solve the problem when interfacing with (many)
external C++ functions taking structs (represented in D by structs as
well) by (mostly const) ref. You're forced to declare lvalues for all of
these args, uglifying the code substantially.
You can add additional overloads on the D side. (This can even be
automated using a string mixin.)
