Add support for ranges, containers and tuple-like types in fmt/ranges.h

include/fmt/ranges.h

+// Formatting library for C++ - the core API
+//
+// Copyright (c) 2012 - present, Victor Zverovich
+// All rights reserved.
+//
+// For the license information refer to format.h.
+//
+// Copyright (c) 2018 - present, Remotion (Igor Schulz)
+// All Rights Reserved
+// {fmt} support for ranges, containers and types tuple interface.
+
+#ifndef FMT_RANGES_H_
+#define FMT_RANGES_H_
+
+#include "format.h"
+#include <type_traits>
+
+// output only up to N items from the range.
+#ifndef FMT_RANGE_OUTPUT_LENGTH_LIMIT
+# define FMT_RANGE_OUTPUT_LENGTH_LIMIT 256
+#endif
+
+FMT_BEGIN_NAMESPACE
+
+template <typename Char>
+struct formatting_base {
+  template <typename ParseContext>
+  FMT_CONSTEXPR auto parse(ParseContext &ctx) -> decltype(ctx.begin()) {
+    return ctx.begin();
+  }
+};
+
+template <typename Char, typename Enable = void>
+struct formatting_range : formatting_base<Char> {
+  static FMT_CONSTEXPR_DECL const std::size_t range_length_limit =
+      FMT_RANGE_OUTPUT_LENGTH_LIMIT; // output only up to N items from the range.
+  Char prefix = '{';
+  Char delimiter = ',';
+  Char postfix = '}';
+  static FMT_CONSTEXPR_DECL const bool add_delimiter_spaces = true;
+  static FMT_CONSTEXPR_DECL const bool add_prepostfix_space = false;
+};
+
+template <typename Char, typename Enable = void>
+struct formatting_tuple : formatting_base<Char> {
+  Char prefix = '(';
+  Char delimiter = ',';
+  Char postfix = ')';
+  static FMT_CONSTEXPR_DECL const bool add_delimiter_spaces = true;
+  static FMT_CONSTEXPR_DECL const bool add_prepostfix_space = false;
+};
+
+namespace internal {
+
+template <typename RangeT, typename OutputIterator>
+void copy(const RangeT &range, OutputIterator out) {
+  for (const auto &it : range) {
+    *out++ = it;
+  }
+}
+
+template <typename OutputIterator>
+void copy(const char *str, OutputIterator out) {
+  const char *p_curr = str;
+  while (*p_curr) {
+    *out++ = *p_curr++;
+  }
+}
+
+template <typename OutputIterator>
+void copy(char ch, OutputIterator out) {
+  *out++ = ch;
+}
+
+/// Return true value if T has std::string interface, like std::string_view.
+template <typename T>
+class is_like_std_string {
+  template <typename U>
+  static auto check(U *p) ->
+    decltype(p->find('a'), p->length(), p->data(), int());
+  template <typename>
+  static void check(...);
+
+ public:
+  static FMT_CONSTEXPR_DECL const bool value =
+    !std::is_void<decltype(check<T>(nullptr))>::value;
+};
+
+template <typename... Ts>
+struct conditional_helper {};
+
+template <typename T, typename _ = void>
+struct is_range_ : std::false_type {};
+
+template <typename T>
+struct is_range_<T,typename std::conditional<
+                   false,
+                   conditional_helper<decltype(std::declval<T>().begin()),
+                                      decltype(std::declval<T>().end())>,
+                   void>::type> : std::true_type {};
+
+template <typename T>
+struct is_range {
+  static FMT_CONSTEXPR_DECL const bool value =
+    is_range_<T>::value && !is_like_std_string<T>::value;
+};
+
+/// tuple_size and tuple_element check.
+template <typename T>
+class is_tuple_like_ {
+  template <typename U>
+  static auto check(U *p) ->
+    decltype(std::tuple_size<U>::value,
+             std::declval<typename std::tuple_element<0, U>::type>(), int());
+  template <typename>
+  static void check(...);
+
+ public:
+  static FMT_CONSTEXPR_DECL const bool value =
+    !std::is_void<decltype(check<T>(nullptr))>::value;
+};
+
+template <typename T>
+struct is_tuple_like {
+  static FMT_CONSTEXPR_DECL const bool value =
+    is_tuple_like_<T>::value && !is_range_<T>::value;
+};
+
+template <size_t... Is, class Tuple, class F>
+void for_each(std::index_sequence<Is...>, Tuple &&tup, F &&f) noexcept {
+  using std::get;
+  // using free function get<I>(T) now.
+  const int _[] = {0, ((void)f(get<Is>(tup)), 0)...};
+  (void)_;  // blocks warnings
+}
+
+template <class T>
+FMT_CONSTEXPR std::make_index_sequence<std::tuple_size<T>::value> 
+get_indexes(T const &) { return {}; }
+
+template <class Tuple, class F>
+void for_each(Tuple &&tup, F &&f) {
+  const auto indexes = get_indexes(tup);
+  for_each(indexes, std::forward<Tuple>(tup), std::forward<F>(f));
+}
+}  // namespace internal
+
+template <typename TupleT, typename Char>
+struct formatter<TupleT, Char, 
+    typename std::enable_if<fmt::internal::is_tuple_like<TupleT>::value>::type> {
+
+  fmt::formatting_tuple<Char> formatting;
+
+  template <typename ParseContext>
+  FMT_CONSTEXPR auto parse(ParseContext &ctx) -> decltype(ctx.begin()) {
+    return formatting.parse(ctx);
+  }
+
+  template <typename FormatContext = format_context>
+  auto format(const TupleT &values, FormatContext &ctx) -> decltype(ctx.out()) {
+    auto out = ctx.out();
+    std::size_t i = 0;
+    internal::copy(formatting.prefix, out);
+    internal::for_each(values, [&](const auto &v) {
+      if (i > 0) {
+        if (formatting.add_prepostfix_space) {
+          *out++ = ' ';
+        }
+        internal::copy(formatting.delimiter, out);
+      }
+      if (formatting.add_delimiter_spaces && i > 0) {
+        format_to(out, " {}", v);
+      } else {
+        format_to(out, "{}", v);
+      }
+      ++i;
+    });
+    if (formatting.add_prepostfix_space) {
+      *out++ = ' ';
+    }
+    internal::copy(formatting.postfix, out);
+
+    return ctx.out();
+  }
+};
+
+template <typename RangeT, typename Char>
+struct formatter< RangeT, Char,
+    typename std::enable_if<fmt::internal::is_range<RangeT>::value>::type> {
+
+  fmt::formatting_range<Char> formatting;
+
+  template <typename ParseContext>
+  FMT_CONSTEXPR auto parse(ParseContext &ctx) -> decltype(ctx.begin()) {
+    return formatting.parse(ctx);
+  }
+
+  template <typename FormatContext>
+  auto format(const RangeT &values, FormatContext &ctx) -> decltype(ctx.out()) {
+    auto out = ctx.out();
+    internal::copy(formatting.prefix, out);
+    std::size_t i = 0;
+    for (const auto &it : values) {
+      if (i > 0) {
+        if (formatting.add_prepostfix_space) {
+          *out++ = ' ';
+        }
+        internal::copy(formatting.delimiter, out);
+      }
+      if (formatting.add_delimiter_spaces && i > 0) {
+        format_to(out, " {}", it);
+      } else {
+        format_to(out, "{}", it);
+      }
+      if (++i > formatting.range_length_limit) {
+        format_to(out, " ... <other elements>");
+        break;
+      }
+    }
+    if (formatting.add_prepostfix_space) {
+      *out++ = ' ';
+    }
+    internal::copy(formatting.postfix, out);
+    return ctx.out();
+  }
+};
+
+FMT_END_NAMESPACE
+
+#endif // FMT_RANGES_H_
+

test/CMakeLists.txt

@@ -92,6 +92,7 @@ add_fmt_test(printf-test)
 add_fmt_test(time-test)
 add_fmt_test(util-test mock-allocator.h)
 add_fmt_test(custom-formatter-test)
+add_fmt_test(ranges-test)
 
 # Enable stricter options for one test to make sure that the header is free of
 # warnings.

test/ranges-test.cc

+// Formatting library for C++ - the core API
+//
+// Copyright (c) 2012 - present, Victor Zverovich
+// All rights reserved.
+//
+// For the license information refer to format.h.
+//
+// Copyright (c) 2018 - present, Remotion (Igor Schulz)
+// All Rights Reserved
+// {fmt} support for ranges, containers and types tuple interface.
+
+#include "fmt/ranges.h"
+
+#include "gtest/gtest.h"
+
+#include <vector>
+#include <array>
+#include <map>
+#include <string>
+
+TEST(RangesTest, FormatVector) {
+  std::vector<int32_t> iv{1, 2, 3, 5, 7, 11};
+  auto ivf = fmt::format("{}", iv);
+  EXPECT_EQ("{1, 2, 3, 5, 7, 11}", ivf);
+}
+
+TEST(RangesTest, FormatVector2) {
+  std::vector<std::vector<int32_t>> ivv{{1, 2}, {3, 5}, {7, 11}};
+  auto ivf = fmt::format("{}", ivv);
+  EXPECT_EQ("{{1, 2}, {3, 5}, {7, 11}}", ivf);
+}
+
+TEST(RangesTest, FormatMap) {
+  std::map<std::string, int32_t> simap{{"one", 1}, {"two", 2}};
+  EXPECT_EQ("{(one, 1), (two, 2)}", fmt::format("{}", simap));
+}
+
+TEST(RangesTest, FormatPair) {
+  std::pair<int64_t, float> pa1{42, 3.14159265358979f};
+  EXPECT_EQ("(42, 3.14159)", fmt::format("{}", pa1));
+}
+
+TEST(RangesTest, FormatTuple) {
+  std::tuple<int64_t, float, std::string> tu1{42, 3.14159265358979f,
+                                              "this is tuple"};
+  EXPECT_EQ("(42, 3.14159, this is tuple)", fmt::format("{}", tu1));
+}
+
+/// check if  'if constexpr' is supported.
+#if (__cplusplus > 201402L) || \
+    (defined(_MSVC_LANG) && _MSVC_LANG > 201402L && _MSC_VER >= 1910)
+
+struct my_struct {
+  int32_t i;
+  std::string str;  // can throw
+  template <std::size_t N>
+  decltype(auto) get() const noexcept {
+    if constexpr (N == 0)
+      return i;
+    else if constexpr (N == 1)
+      return fmt::string_view{str};
+  }
+};
+
+template <std::size_t N>
+decltype(auto) get(const my_struct& s) noexcept {
+  return s.get<N>();
+}
+
+namespace std {
+
+template <>
+struct tuple_size<my_struct> : std::integral_constant<std::size_t, 2> {};
+
+template <std::size_t N>
+struct tuple_element<N, my_struct> {
+  using type = decltype(std::declval<my_struct>().get<N>());
+};
+
+}  // namespace std
+
+TEST(RangesTest, FormatStruct) {
+  my_struct mst{13, "my struct"};
+  EXPECT_EQ("(13, my struct)", fmt::format("{}", mst));
+}
+
+#endif  // (__cplusplus > 201402L) || (defined(_MSVC_LANG) && _MSVC_LANG >
+        // 201402L && _MSC_VER >= 1910)