only use stream for serialisation

include/sp/protocol/message/OstreamFieldIterator.h

@@ -0,0 +1,50 @@
+// infix_iterator.h
+//
+// Lifted from Jerry Coffin's 's prefix_ostream_iterator
+#pragma once
+
+#include <iterator>
+#include <ostream>
+#include <sp/protocol/Field.h>
+
+namespace sp {
+
+template <class T, class charT = char, class traits = std::char_traits<charT>>
+class OstreamFieldIterator : public std::iterator<std::output_iterator_tag, void, void, void, void> {
+  private:
+	std::basic_ostream<charT, traits>* m_Os;
+	std::string m_Delimiter;
+	bool m_FirstElem;
+
+  public:
+	typedef charT char_type;
+	typedef traits traits_type;
+	typedef std::basic_ostream<charT, traits> ostream_type;
+	OstreamFieldIterator(ostream_type& a_Stream) : m_Os(&a_Stream), m_Delimiter(0), m_FirstElem(true) {}
+	OstreamFieldIterator(ostream_type& a_Stream, std::string&& a_Delimiter) :
+		m_Os(&a_Stream), m_Delimiter(std::move(a_Delimiter)), m_FirstElem(true) {}
+
+	auto& operator=(const T& item) {
+		// Here's the only real change from ostream_iterator:
+		// Normally, the '*m_Os << item;' would come before the 'if'.
+		if (!m_FirstElem && !m_Delimiter.empty())
+			*m_Os << m_Delimiter;
+		*m_Os << sp::PrintableField<T>(item);
+		m_FirstElem = false;
+		return *this;
+	}
+
+	auto& operator*() {
+		return *this;
+	}
+
+	auto& operator++() {
+		return *this;
+	}
+
+	auto& operator++(int) {
+		return *this;
+	}
+};
+
+}  // namespace sp