I tried to calculate the factorial of an integer with templates,
the D compiler did not like it.

Is recursion not allowed in D templates?

bye,
roel

// -------------------------------------------------------
// first attempt: with specialisation it would not compile
// corrected the little error :-) scusi
template factor(int n)
{	
	int value()
	{
		return n * factor!(n-1).value();
	}
}

template factor(int n : 0)
{
	int value()
	{
		return 1;
	}
}
template factor(int n : 1)
{
	int value()
	{
		return 1;
	}
}

int main()
{
	printf( "%d\n"
		  , factor!(4).value()
		  );

	return 0;
}

// -------------------------------------------------------
// second attempt: testing for end condition
// 	=> going ballistic
//	=> bug in compiler
template factor(int n)
{	
	int value()
	{
		if (n==0 || n==1) return 1;
		return n * factor!(n-1).value();
	}
}

int main()
{
	printf( "%d\n"
		  , factor!(4).value()
		  );

	return 0;
}

Well the tradtional C++ way caused
dmd to blow up.

template factor(int n : 1)
{
  enum { value = 1 }
}

template factor(int n)
{
  enum { value = n*factor!(n-1).value }
}


int main(char[][] argv)
{

  int i = factor!(3).value;

  printf("%d\n",i);

  return 0;

}

This method give the error:
examp.d(5): non-constant expression 3 * value


template factor(int n : 1)
{
  const int value = 1;
}

template factor(int n)
{
  const int value = n*factor!(n-1).value;
}


int main(char[][] argv)
{

  int i = factor!(3).value;

  printf("%d\n",i);

  return 0;

}






Roel Mathys <roel.mathys@yucom.be> wrote in news:bubp7v$2h6n$1 @digitaldaemon.com:

> I tried to calculate the factorial of an integer with templates, the D compiler did not like it.
> 
> Is recursion not allowed in D templates?
> 
> bye,
> roel
> 
> // -------------------------------------------------------
> // first attempt: with specialisation it would not compile
> // corrected the little error :-) scusi
> template factor(int n)
> {
>      int value()
>      {
>           return n * factor!(n-1).value();
>      }
> }
> 
> template factor(int n : 0)
> {
>      int value()
>      {
>           return 1;
>      }
> }
> template factor(int n : 1)
> {
>      int value()
>      {
>           return 1;
>      }
> }
> 
> int main()
> {
>      printf( "%d\n"
>             , factor!(4).value()
>             );
> 
>      return 0;
> }
> 
> // -------------------------------------------------------
> // second attempt: testing for end condition
> //      => going ballistic
> //     => bug in compiler
> template factor(int n)
> {
>      int value()
>      {
>           if (n==0 || n==1) return 1;
>           return n * factor!(n-1).value();
>      }
> }
> 
> int main()
> {
>      printf( "%d\n"
>             , factor!(4).value()
>             );
> 
>      return 0;
> }