intermediate changes

ref:cde9a383711a11544ce7e107a78147fb96cc4029

1 files changed, 70 insertions, 0 deletions

diff --git a/library/cpp/yt/misc/variant-inl.h b/library/cpp/yt/misc/variant-inl.h
new file mode 100644
index 0000000000..fb7d98d4be
--- /dev/null
+++ b/library/cpp/yt/misc/variant-inl.h
@@ -0,0 +1,70 @@
+#ifndef VARIANT_INL_H_
+#error "Direct inclusion of this file is not allowed, include variant.h"
+// For the sake of sane code completion.
+#include "variant.h"
+#endif
+
+#include <type_traits>
+
+namespace NYT {
+
+////////////////////////////////////////////////////////////////////////////////
+
+namespace NDetail {
+
+template <class T>
+struct TIndexOf<T>
+{
+    static constexpr size_t Value = std::numeric_limits<size_t>::max();
+};
+
+template <class T, class T0, class... Ts>
+struct TIndexOf<T, T0, Ts...>
+{
+    static constexpr size_t Value = std::is_same_v<T, T0>
+        ? 0
+        : 1 + TIndexOf<T, Ts...>::Value;
+};
+
+template <size_t Index, class... Ts>
+struct TVariantFormatter;
+
+template <size_t Index>
+struct TVariantFormatter<Index>
+{
+    template <class TVariant>
+    static void Do(TStringBuilderBase* /*builder*/, const TVariant& /*variant*/, TStringBuf /*spec*/)
+    { }
+};
+
+template <size_t Index, class T, class... Ts>
+struct TVariantFormatter<Index, T, Ts...>
+{
+    template <class TVariant>
+    static void Do(TStringBuilderBase* builder, const TVariant& variant, TStringBuf spec)
+    {
+        if (variant.index() == Index) {
+            FormatValue(builder, std::get<Index>(variant), spec);
+        } else {
+            TVariantFormatter<Index + 1, Ts...>::Do(builder, variant, spec);
+        }
+    }
+};
+
+} // namespace NDetail
+
+template <class... Ts>
+void FormatValue(TStringBuilderBase* builder, const std::variant<Ts...>& variant, TStringBuf spec)
+{
+    NDetail::TVariantFormatter<0, Ts...>::Do(builder, variant, spec);
+}
+
+template <class... Ts>
+TString ToString(const std::variant<Ts...>& variant)
+{
+    return ToStringViaBuilder(variant);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+} // namespace NYT