Is instantiabilty of templated types decidable?

[Rob T]

On Sunday, 11 November 2012 at 20:40:35 UTC, Nick Sabalausky 
wrote:
>> The possible inputs are finite, so the property is decidable.
>
> Technically, yea, but I think upwards of ~4 billion template
> instantiations is quite unrealistic, to the point of being 
> effectively
> undecidable.

My thoughts exactly. Using the template system in this way looks 
like abuse rather than being practical. There must be alternative 
methods to get the same results for whatever you may be 
attempting.

What we could do is set a practical limit of some default number. 
500 appears to be the default limit right now, although in 
reality without an official written spec we have nothing specific 
to expect and rely on.

I do agree with manfred that the limit is arbitrary and there may 
be a few valid use cases where the number should be user 
adjustable.

--rt