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D - DMD compiler does not like template recursion

reply Roel Mathys <roel.mathys yucom.be> writes:
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;
}
Jan 17 2004
parent Patrick Down <pat codemoon.com> writes:
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;
 }

Jan 17 2004