code: private int extractMatchingFields(Tuple<Type.Field> lhsFields, Tuple<Type.Field> rhsFields, Type.Field[] result,
  			LifetimeRelation lifetimes, LinkageStack stack) {
  		int index = 0;
  		// Extract all matching fields first.
  		for (int i = 0; i != lhsFields.size(); ++i) {
  			for (int j = 0; j != rhsFields.size(); ++j) {
  				Type.Field lhsField = lhsFields.get(i);
  				Type.Field rhsField = rhsFields.get(j);
  				Identifier lhsFieldName = lhsField.getName();
  				Identifier rhsFieldName = rhsField.getName();
  				if (lhsFieldName.equals(rhsFieldName)) {
  					Type type = apply(lhsField.getType(), rhsField.getType(), lifetimes, stack);
  					Type.Field combined = new Type.Field(lhsFieldName, type);
  					result[index++] = combined;
  				}
  			}
  		}
  		return index;
  	}
docs: Extract all matching fields (i.e. fields with the same name) into the result
  array.
  
  @param lhsFields
  @param rhsFields
  @param result
  @return