From bf4f1a256ef17c1c640670ef78523f5160dd23e4 Mon Sep 17 00:00:00 2001
From: "Dr. Patrick Urbanke" <patrick@getml.com>
Date: Sat, 22 Mar 2025 03:25:51 +0100
Subject: [PATCH] Added an Iterator

---
 include/Connection.hpp |  6 +++---
 include/Iterator.hpp   | 25 +++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 3 deletions(-)
 create mode 100644 include/Iterator.hpp

diff --git a/include/Connection.hpp b/include/Connection.hpp
index 7d7ce32..7995f42 100644
--- a/include/Connection.hpp
+++ b/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.
diff --git a/include/Iterator.hpp b/include/Iterator.hpp
new file mode 100644
index 0000000..dfcf751
--- /dev/null
+++ b/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