alias_this_assignment.dd

End deprecation period for using `alias this` for partial assignment.

Starting with this release, `alias this` may not be used for the partial
assignment of a left-hand side operand. Any such assignment will result in a
compiler error.

If a struct has a single member which is aliased this directly or aliased to a
ref getter function that returns the mentioned member, then alias this may be
used since the object will be fully initialised.

---
struct Allowed
{
    int onemember;
    alias onemember this;
}

struct Rejected
{
    int aliased;
    long other;
    alias aliased this;
}

void fun(Allowed a, Rejected r)
{
    a = 0; // OK, struct has only one member.
    r = 0; // Error, cannot use `alias this` to partially initialize variable `r` of type `Rejected`. Use `r.aliased`
}
---