struct opCmp confustion

[Charles Hixson]

Currently the code is:

struct	Triplet
{	string	wrd1;
	string	wrd2;
	string	wrd3;
	int		val	=	1;

	int opCmp(ref const Triplet t) const
	{	if	(wrd1 < t.wrd1)	return	-1;
		if	(wrd1 > t.wrd1)	return	1;
		if	(wrd2 < t.wrd2)	return	-1;
		if	(wrd2 > t.wrd2)	return	1;
		if	(wrd3 < t.wrd3)	return	-1;
		if	(wrd3 > t.wrd3)	return	1;
		return	0;
		//auto	i	=	wrd1.opCmp (t.wrd1);
		//if	(i !=	0)	return	i;
		//i	=	wrd2.opCmp (t.wrd2);
		//if	(i != 0)	return	i;
		//return	wrd3.opCmp (t.wrd3);
	}
}
The commented out code was the original version, which wouldn't compile. 
  (The current code replaces it.) It gave messages like:
...ser$ rdmd --main -unittest -DdDocs parse1.d
parse1.d(114): Error: undefined identifier 'opCmp'
parse1.d(116): Error: undefined identifier 'opCmp'
parse1.d(118): Error: undefined identifier 'opCmp'

What was I doing wrong?