Truly algebraic Variant and Nullable

[9il]

On Tuesday, 22 December 2020 at 14:27:02 UTC, ag0aep6g wrote:
> On 22.12.20 04:56, 9il wrote:
>> 6. Algebraic type subsets are supported by `get`, 
>> `trustedGet`, `_is`, and `this` primitives. You can operate 
>> with algebraic subset as with the type of the original 
>> typeset. [1]
>
> "trustedGet" - That name smells of a safety violation. And 
> indeed (compile with `-release`):

> The normal `get` also violates safety by giving out references 
> into the union (compile with `-preview=dip1000`):

> But that might be an issue with DIP1000. `ref_to_ptr` is a hint 
> that something isn't right in that area.

The definitions are

```
auto ref get(E)() @property return inout
auto ref trustedGet(E)() @trusted @property return inout nothrow
```

Both market with `return`.

According to the spec [1, example 2]

"Struct non-static methods marked with the return attribute 
ensure the returned reference will not outlive the struct 
instance."

The docs maybe not clear enough. `trustedGet` asserts type is 
matched, while `get` throws an exception if the type doesn't 
match.

[1] https://dlang.org/spec/function.html#return-ref-parameters