On Friday, 4 May 2018 at 09:34:14 UTC, Jonathan M Davis wrote:
[...]
It's actually not infrequent now that in C++, you want to pass
stuf by value rather than const& precisely because move
semantics can be used to avoid copies. So, it's not at all
necessarily the case that passing by ref is the efficient thing
to do. It's heavily dependent on the code in question.
I once proposed that `in` can mean `const scope ref` that also
binds rvalues.
https://github.com/dlang/DIPs/pull/111#issuecomment-381911140
We could make `in` be something similar to `inline`. The compiler
can implement it as stated above (assign the expression to
temporary, reference it), or use copy if copy is cheaper than
referencing.
So, even if we were designing in from scratch, making ref would
be a questionable choice. However, even if we all agreed that
it would be desirable, such a change would break a large
percentage of code that currently uses in, because any code
that passes an rvalue to a function taking its argument as in
would then break. So, any attempt to change in to include ref
would have to have some sort of deprecation path to avoid code
breakage. But given how annoying it would be to have in be ref
by default due to how that affects rvalues, I'm willing to bet
that most programmers would not be at all happy with such a
change, regardless of how well the transitition was handled.
Yes. Therefore the idea above. It will break much less code if
any.
