> function arguments can be "in", "out", "inout", "ref", "scope", "return ref" - and combinations.

None of them are required. What they do is provide enforcement of semantics that otherwise would have to be put in the documentation. And, as we all know, function documentation is always either missing, outdated or just plain wrong.

For a (trivial) example:

    void foo(int* p) { *p = 3; }

    void foo(out int i) { i = 3; }

`out` definitely is a win. Let's look at `scope`:

    void foo(int* p) { static int* pg = p; }
    void bar(*) {
        int x;
        foo(&x); // oops
    }

This is most definitely a memory safety feature.