On Sunday, 30 December 2012 at 08:38:27 UTC, Jonathan M Davis
wrote:
After some recent discussions relating to auto ref and const
ref, I have come
to the conlusion that as it stands, ref is not @safe. It's
@system. And I
think that we need to take a serious look at it to see what we
can do to make
it @safe. The problem is combining code that takes ref
parameters with code
that returns by ref.
The best solution I can think of is for the @safe code to require
a ref return value is treated with the same care as all the
function input arguments. I'll try to annotate the example code
you gave to explain.
Take this code for example:
ref int foo(ref int i)
{
return i;
}
This function is valid. Ref input arguments can be returned.
ref int bar()
{
int i = 7;
return foo(i);
}
If @safe, this code will not compile.
Error: foo may return a local stack variable
Since "i" is a local variable, "foo(i)" might return it.
ref int baz(int i)
{
return foo(i);
}
This function is fine. "i" is an input argument so "foo(i)" is
considered to be equivalent to an input argument.
void main()
{
auto a = bar();
auto b = baz(5);
}
Both function calls compile. The variable a could be returned.
I'm not sure if b should be returnable by ref. if "5" is a
manifest constant, it must be an error in @safe code. If it has a
permanent address, it could be returned.
