Recursive templated structs disallowed?

[Simen kjaeraas]

Steven Schveighoffer <schveiguy at yahoo.com> wrote:

> On Wed, 04 Aug 2010 15:37:32 -0400, Simen kjaeraas  
> <simen.kjaras at gmail.com> wrote:
>
>> struct bar( T ) {
>>      auto baz( U )( U arg ) {
>>          bar!( typeof( this ) ) tmp;
>>          return tmp;
>>      }
>> }
>>
>> void main( ) {
>>      bar!int n;
>>      n.baz( 3 );
>> }
>>
>> This code fails with
>> Error: recursive template expansion for template argument bar!(int)
>> Now, I agree it is recursive, but it is not infinitely recursive, so
>> there shouldn't really be a problem.
>> Is this a bug? Is there a workaround?
>
> It's lazily recursive.  Meaning, it *is* infinitely recursive, but the  
> compiler does not have to evaluate all the recursions until they are  
> used.
>
> I'm not sure it should be disallowed, but it's definitely on the edge.   
> Do you have some real-world case for this?  If you want to get something  
> like this fixed, you'll need a good example, not an academic one.

I sorta do. I have a struct that keeps track of the operations performed
on it, to create a template stack for calculating stuff at the end.
Basically, I build a function by performing the operations on the
struct. Not sure if this is an expression template, but possibly related.

-- 
Simen