On 11/11/2012 03:45 PM, Peter Alexander wrote:
On Sunday, 11 November 2012 at 13:40:45 UTC, evansl wrote:
On 11/11/12 06:49, Peter Alexander wrote:
On Sunday, 11 November 2012 at 12:33:25 UTC, Manfred Nowak wrote:
a) Instantiability is decidable
Why does the compiler stop with the evaluation at that randomly
choosen and apparently hard coded value of 500 recursive
expansions?
It's not decidable. Consider use of static if. It's Turing complete. I
can give an example if you like.
I'd like. An example might help me better understand why it's
undecidable.
[snip]
Collatz sequence.
struct Collatz(int n)
{
enum next = n % 2 == 0 ? n / 2 : 3 * n + 1;
Collatz!(next)* foo;
}
It's an unsolved problem in mathematics whether or not this instantiates
an infinite number of templates.
The possible inputs are finite, so the property is decidable.
