Added an Iterator

include/Connection.hpp

@@ -4,6 +4,7 @@
 #include <string>
 #include <vector>
 
+#include "Iterator.hpp"
 #include "Result.hpp"
 #include "dynamic/CreateTable.hpp"
 #include "dynamic/Insert.hpp"
@@ -15,12 +16,11 @@ namespace sqlgen {
 /// database connections.
 struct Connection {
   /// Executes a statement.
-  /// TODO: Abstract away the different statements using a lambda function.
+  /// TODO: Abstract away the different statements using rfl::TaggedUnion.
   virtual Result<Nothing> execute(const CreateTable& _stmt) = 0;
 
   /// Reads the results of a SelectFrom statement.
-  virtual Result<std::vector<std::vector<std::string>>> read(
-      const dynamic::SelectFrom& _query) = 0;
+  virtual Result<Iterator> read(const dynamic::SelectFrom& _query) = 0;
 
   /// Writes data into a table. Each vector in data MUST have the same length as
   /// _stmt.columns.

include/Iterator.hpp

@@ -0,0 +1,25 @@
+#ifndef SQLGEN_ITERATOR_HPP_
+#define SQLGEN_ITERATOR_HPP_
+
+#include <string>
+#include <vector>
+
+#include "Result.hpp"
+
+namespace sqlgen {
+
+/// Abstract base class for an iterator to be returned by Connection::read(...).
+struct Iterator {
+  /// Whether the end of the available data has been reached.
+  virtual bool end() const = 0;
+
+  /// Returns the next batch of rows.
+  /// If _batch_size is greater than the number of rows left, returns all
+  /// of the rows left.
+  virtual Result<std::vector<std::vector<std::string>>> next(
+      const size_t _batch_size) = 0;
+};
+
+}  // namespace sqlgen
+
+#endif