Unexpectedly nice case of auto return type

[Basile B.]

On Tuesday, 3 December 2019 at 07:12:18 UTC, Basile B. wrote:
> I wish something like this was possible, until I change the 
> return type of `alwaysReturnNull` from `void*` to `auto`.
>
>
> ---
> class A {}
> class B {}
>
> auto alwaysReturnNull() // void*, don't compile
> {
>     writeln();
>     return null;
> }
>
> A testA()
> {
>     return alwaysReturnNull();
> }
>
> B testB()
> {
>     return alwaysReturnNull();
> }
>
> void main()
> {
>     assert( testA() is null );
>     assert( testB() is null );
> }
> ---
>
> OMG, isn't it nice that this works ?
>
> I think that this illustrates an non intuitive behavior of auto 
> return types.
> One would rather expect auto to work depending on the inner 
> return type.

Actually I think this can work because of a Tnull (internal 
compiler type) inference which can always implictly be converted 
to the static return type (A or B, or even int*):

     auto alwaysReturnNull()// `auto` is translated to Tnull by 
inference because of `return null`

then:

     A testA()
     {
         return alwaysReturnNull(); // Tnull can be implictly 
converted to A
     }

still nice tho.