On Sunday, 23 October 2016 at 06:36:21 UTC, Jonathan M Davis
wrote:
You can mark a parameter as ref, and you get something similar
to C++'s &, except that it only works on parameters, return
types, and the variable for the current element in a foreach
loop (you can't declare local variables that are ref), and ref
parameters only ever accept lvalues, even if they're const. e.g.
void foo(ref int i) {...}
ref int bar() { return _i; }
foreach(i, ref e; arr) {...}
I think that most D code just passes structs around without
worrying about the cost of copying unless the struct is
particularly large or profiling has shown that copying it is
too expensive. For a lot of stuff, it simply isn't a problem.
And when it is, there's ref, or the struct can be put on the
heap and passed around by pointer. But because we don't have an
equivalent for const& that accepts rvalues, using ref simply to
avoid copying can get annoying. So, it doesn't make much sense
to do it unless it's actually necessary (whereas a lot of C++
code does it just in case it matters).
There is talk of possibly adding a way to pass rvalues by ref
in D, in which case, you would get something similar to C++
const&, but there are problems caused by C++'s approach that we
don't want in D, and D's const is enough more restrictive than
C++ const that whatever we do can't be tied to const.
- Jonathan M Davis
There is still the way to use an universal rvalue => lvalue
conversion function.
