On Monday, 2 March 2015 at 20:54:20 UTC, Walter Bright wrote:
I looked at how Rust does it. I was hoping it was something
clever, but it isn't. A copy is made of the object to which a
borrowed reference is taken - in other words, the reference
count is incremented.
For D structs, that means, if there's a postblit, a copy must
be made. For D ref counted classes, a ref count increment must
be done.
I was hoping to avoid that, but apparently there's no way.
There are cases where this can be avoided, like calling pure
functions. Another win for pure functions!
I do think you are confusing how Rust does it. In Rust, borrowing
makes the source and borrowed reference immutable by default. So
by default the problem do not occurs.
You can also borrow a mutable reference, in which case the source
is disabled for the duration of the borrowing. That makes it
impossible to borrow a mutable reference twice.
The above mentioned scenario cannot happen at all in Rust, by
design. As a result, there is solution for the problem, as the
problem cannot occur in the first place.
