struct Foo
{
    @property void x(int) {}
}

struct Bar
{
    Foo foo;
    
    void opDispatch(string Field, Args...)(Args args)
    {
        foo.x = args;
    }
}

void main()
{
    Bar bar;
    bar.x = 5;
}

Error: expected 1 function arguments, not 0

Of course there's no way DMD can tell in advance that opDispatch will invoke a property function, so it just expects opDispatch to return an lvalue to be assigned with 5. :/