Implement deleting sets from the db.

include/helpers/infix_iterator.hpp

@@ -0,0 +1,48 @@
+// see http://stackoverflow.com/questions/3496982/printing-lists-with-commas-c/3497021#3497021
+// infix_iterator.h
+//
+// Lifted from Jerry Coffin's 's prefix_ostream_iterator
+#if !defined(INFIX_ITERATOR_H_)
+#define  INFIX_ITERATOR_H_
+#include <ostream>
+#include <iterator>
+template <class T,
+          class charT=char,
+          class traits=std::char_traits<charT> >
+class infix_ostream_iterator :
+    public std::iterator<std::output_iterator_tag,void,void,void,void>
+{
+    std::basic_ostream<charT,traits> *os;
+    charT const* delimiter;
+    bool first_elem;
+public:
+    typedef charT char_type;
+    typedef traits traits_type;
+    typedef std::basic_ostream<charT,traits> ostream_type;
+    infix_ostream_iterator(ostream_type& s)
+        : os(&s),delimiter(0), first_elem(true)
+    {}
+    infix_ostream_iterator(ostream_type& s, charT const *d)
+        : os(&s),delimiter(d), first_elem(true)
+    {}
+    infix_ostream_iterator<T,charT,traits>& operator=(T const &item)
+    {
+        // Here's the only real change from ostream_iterator:
+        // Normally, the '*os << item;' would come before the 'if'.
+        if (!first_elem && delimiter != 0)
+            *os << delimiter;
+        *os << item;
+        first_elem = false;
+        return *this;
+    }
+    infix_ostream_iterator<T,charT,traits> &operator*() {
+        return *this;
+    }
+    infix_ostream_iterator<T,charT,traits> &operator++() {
+        return *this;
+    }
+    infix_ostream_iterator<T,charT,traits> &operator++(int) {
+        return *this;
+    }
+};
+#endif