Please do not use 'auto' return types without thoroughly describing the interface

[rikki cattermole]

I would like to fix this using signatures[0].
Signatures have a number of benefits here, including removing of 
TypeInfo (which prevents code-bloat).

There is a few other examples based upon allocators here[1].

But this isn't a short term goal even if it does get approved ;)

[0] https://github.com/rikkimax/DIPs/blob/master/DIPs/DIP1xxx-RC.md
[1] 
https://github.com/rikkimax/stdc-signatures/blob/master/stdc/memory/allocators.d