Without using decltype

[EwCjE3v7]

How would you write the following without using decltype?

  multiset<Sales_data, decltype(compareIsbn*> bookstore(compareIsbn

CompareIsbn

  bool campareIsbn(const Sales_ &lhs, const Sales_data &rhs)
{
	return lhs.isbn() < rhs.isbnt();
}

[JLBorges]

using cmp_fn_type = bool( const Sales_data&, const Sales_data& ) ;
std::multiset< Sales_data, cmp_fn_type* > bookstore(compareIsbn) ;

or just
std::multiset< Sales_data, bool(*)( const Sales_data&, const Sales_data& ) > bookstore(compareIsbn) ;

[EwCjE3v7]

Thanks JLBorges