From a63a24f2d7d9a425c20857e7089d54a3cf8789d2 Mon Sep 17 00:00:00 2001
From: Dean Moldovan <dean0x7d@gmail.com>
Date: Sun, 27 Sep 2015 02:26:26 +0200
Subject: [PATCH] Add _format literal

---
 format.h            | 38 ++++++++++++++++++++++++++++++++++++++
 test/format-test.cc |  9 +++++++++
 2 files changed, 47 insertions(+)

diff --git a/format.h b/format.h
index 8260024f..b85ddcb1 100644
--- a/format.h
+++ b/format.h
@@ -177,6 +177,16 @@ inline uint32_t clzll(uint64_t x) {
     TypeName& operator=(const TypeName&)
 #endif
 
+#ifndef FMT_USE_USER_DEFINED_LITERALS
+// All compilers which support UDLs also support variadic templates. This
+// makes the fmt::literals implementation easier. However, an explicit check
+// for variadic templates is added here just in case.
+# define FMT_USE_USER_DEFINED_LITERALS \
+   FMT_USE_VARIADIC_TEMPLATES && \
+   (FMT_HAS_FEATURE(cxx_user_literals) || \
+       (FMT_GCC_VERSION >= 407 && FMT_HAS_GXX_CXX11) || _MSC_VER >= 1900)
+#endif
+
 #ifndef FMT_ASSERT
 # define FMT_ASSERT(condition, message) assert((condition) && message)
 #endif
@@ -3005,6 +3015,34 @@ FMT_VARIADIC(int, printf, CStringRef)
 FMT_VARIADIC(int, fprintf, std::FILE *, CStringRef)
 }
 
+#if FMT_USE_USER_DEFINED_LITERALS
+namespace fmt {
+namespace internal {
+
+template <typename Char>
+struct UdlFormat {
+  const Char *str;
+
+  template <typename... Args>
+  auto operator()(Args && ... args) const
+                  -> decltype(format(str, std::forward<Args>(args)...)) {
+    return format(str, std::forward<Args>(args)...);
+  }
+};
+
+} // namespace internal
+
+inline namespace literals {
+
+inline internal::UdlFormat<char>
+operator"" _format(const char *s, std::size_t) { return {s}; }
+inline internal::UdlFormat<wchar_t>
+operator"" _format(const wchar_t *s, std::size_t) { return {s}; }
+
+} // inline namespace literals
+} // namespace fmt
+#endif // FMT_USE_USER_DEFINED_LITERALS
+
 // Restore warnings.
 #if FMT_GCC_VERSION >= 406
 # pragma GCC diagnostic pop
diff --git a/test/format-test.cc b/test/format-test.cc
index 18498524..b95c499a 100644
--- a/test/format-test.cc
+++ b/test/format-test.cc
@@ -1602,3 +1602,12 @@ TEST(FormatTest, MaxArgs) {
             fmt::format("{}{}{}{}{}{}{}{}{}{}{}{}{}{}{}",
                         0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 'a', 'b', 'c', 'd', 'e'));
 }
+
+#if FMT_USE_USER_DEFINED_LITERALS
+using namespace fmt::literals;
+
+TEST(LiteralsTest, Format) {
+  EXPECT_EQ(format("{}c{}", "ab", 1), "{}c{}"_format("ab", 1));
+  EXPECT_EQ(format(L"{}c{}", L"ab", 1), L"{}c{}"_format(L"ab", 1));
+}
+#endif // FMT_USE_USER_DEFINED_LITERALS