On Monday, 26 March 2018 at 14:40:03 UTC, Atila Neves wrote:
C++ T&& (Rvalue reference) -> D T
Not really, in C++ it is an actual reference and you get to
choose which function actually does the move. In D it just does
the copy when passed to the function. So you can't do this in D.
void bar(T&& t)
{
// actually move contents of T
}
void foo(T&& t)
{
bar(std::forward<T>(t)); // Can't do this in D without making
another actual copy cause it isn't a reference
}
If replacing const T& with T chafes, I understand. I used to
feel that way too. It's _possible_ that would incur a penalty
in copying/moving, but IME the cost is either 0, negligible, or
negative (!).
As mentioned above, if calling C++ code there's no choice about
using T instead of const T&, so for pragmatic reasons that
should be allowed. But only there, because...
Can you please explain these 'weirdities'?
What are said "major unintended consequences"?
Rvalue references. They exist because of being able to bind
temporaries to const T& in C++, which means there's no way of
knowing if your const T& was originally a temporary or not. To
disambiguate C++11 introduced the type system horror that are
rvalue references (which also do double-duty in enabling
perfect forwarding!).
What's a concrete example that you would be required to know
whether a const& is a temporary or not. I don't really see it
otherwise. The solution everyone is saying to use as an
alternative would be the literal case of how it would be
implemented in the language.
D doesn't have or need rvalue references _because_ of not
allowing temporaries to bind to ref const(T). You get move
semantics in D without the pain. That's a win in my book.
Atila
I've come across a few pains of such. It make be easier to use
but it comes at a performance hit. In part binaries become huge
because of how "init" is implemented.
struct StaticArray(T, size_t capacity)
{
size_t length;
T[capacity] values;
}
Copying the above structure copies unnecessary data for any
move/copy operation. Eg when length = 0, it'll still copy
everything. This includes initialization.
