From 91b30e5b4ed57ff4ad43b399c5a761b36fc74325 Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@meta.com>
Date: Sat, 10 Feb 2024 07:38:29 -0800
Subject: [PATCH] More API details

---
 test/scan-test.cc | 12 +++++++++++-
 test/scan.h       | 19 ++++++++++++++-----
 2 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/test/scan-test.cc b/test/scan-test.cc
index 2ff322a7..db27a5b2 100644
--- a/test/scan-test.cc
+++ b/test/scan-test.cc
@@ -110,15 +110,25 @@ TEST(scan_test, invalid_format) {
                    "invalid format string");
 }
 
+namespace std {
+  using fmt::scan;
+  using fmt::scan_error;
+}
+
 TEST(scan_test, example) {
   // Example from https://wg21.link/p1729r3.
-  if (auto result = fmt::scan<std::string, int>("answer = 42", "{} = {}")) {
+  if (auto result = std::scan<std::string, int>("answer = 42", "{} = {}")) {
+    auto range = result->range();
+    EXPECT_EQ(range.begin(), range.end());
+    EXPECT_EQ(result->begin(), result->end());
 #ifdef __cpp_structured_bindings
     const auto& [key, value] = result->values();
     EXPECT_EQ(key, "answer");
     EXPECT_EQ(value, 42);
 #endif
   } else {
+    std::scan_error error = result.error();
+    (void)error;
     FAIL();
   }
 }
diff --git a/test/scan.h b/test/scan.h
index 7e477fed..7e340043 100644
--- a/test/scan.h
+++ b/test/scan.h
@@ -570,9 +570,10 @@ void make_args(std::array<scan_arg, sizeof...(T)>& args,
 }
 }  // namespace detail
 
-template <typename... T> class scan_data {
+template <typename Range, typename... T> class scan_data {
  private:
   std::tuple<T...> values_;
+  Range range_;
 
  public:
   scan_data() = default;
@@ -589,6 +590,11 @@ template <typename... T> class scan_data {
     detail::make_args<0>(args, values_);
     return args;
   }
+
+  auto range() const -> Range { return range_; }
+
+  auto begin() const -> decltype(range_.begin()) { return range_.begin(); }
+  auto end() const -> decltype(range_.end()) { return range_.end(); }
 };
 
 template <typename... T>
@@ -610,10 +616,12 @@ template <typename T, typename E> class expected {
   explicit operator bool() const { return has_value_; }
 
   auto operator->() const -> const T* { return &value_; }
+
+  auto error() -> E const { return E(); }
 };
 
-template <typename... T>
-using scan_result = expected<scan_data<T...>, scan_error>;
+template <typename Range, typename... T>
+using scan_result = expected<scan_data<Range, T...>, scan_error>;
 
 auto vscan(string_view input, string_view fmt, scan_args args)
     -> string_view::iterator {
@@ -630,8 +638,9 @@ auto scan_to(string_view input, string_view fmt, T&... args)
 }
 
 template <typename... T>
-auto scan(string_view input, string_view fmt) -> scan_result<T...> {
-  auto data = scan_data<T...>();
+auto scan(string_view input, string_view fmt)
+    -> scan_result<string_view, T...> {
+  auto data = scan_data<string_view, T...>();
   vscan(input, fmt, data.make_args());
   return data;
 }