bug with auto or what?

[Chris Cain]

On Monday, 13 August 2012 at 19:09:04 UTC, Minas Mina wrote:
> Is it a bug with auto or something else?

It's not really a bug. You're using insert before its return type 
has been inferred. Hence, it says "forward reference to inferred 
return type".

However, in this case, it should be possible to infer the return 
type because they type of root is known. Maybe an enhancement 
request?

In any case, the solution, as you've found, is to explicitly 
define the return type if you're going to be using it recursively.