From 7bca0d82d7ee4f4f2ea4ffe559da7e48265fae2c Mon Sep 17 00:00:00 2001
From: arkady-e1ppa <arkady-e1ppa@yandex-team.com>
Date: Mon, 20 Nov 2023 13:44:15 +0300
Subject: YT-19593: Constexpr friendliness in strong typedef plus TAllocationId
 uses it now

---
 library/cpp/yt/misc/strong_typedef-inl.h | 45 ++++++++++++++++++++++++++++----
 library/cpp/yt/misc/strong_typedef.h     |  6 ++++-
 2 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/library/cpp/yt/misc/strong_typedef-inl.h b/library/cpp/yt/misc/strong_typedef-inl.h
index 0a1bd9427ae..59ff7cbce26 100644
--- a/library/cpp/yt/misc/strong_typedef-inl.h
+++ b/library/cpp/yt/misc/strong_typedef-inl.h
@@ -60,6 +60,32 @@ constexpr T&& TStrongTypedef<T, TTag>::Underlying() &&
     return std::move(Underlying_);
 }
 
+template <class T, class TTag>
+constexpr bool TStrongTypedef<T, TTag>::operator==(const TStrongTypedef& rhs) const
+noexcept(std::same_as<T, void> || noexcept(Underlying_ == rhs.Underlying_))
+{
+    //! NB: We add a constexpr branch to keep constexprness of the function
+    //! without making extra specializations explicitly.
+    if constexpr (std::same_as<T, void>) {
+        return true;
+    }
+
+    return Underlying_ == rhs.Underlying_;
+}
+
+template <class T, class TTag>
+constexpr auto TStrongTypedef<T, TTag>::operator<=>(const TStrongTypedef& rhs) const
+noexcept(std::same_as<T, void> || noexcept(Underlying_ <=> rhs.Underlying_))
+{
+    //! NB: We add a constexpr branch to keep constexprness of the function
+    //! without making extra specializations explicitly.
+    if constexpr (std::same_as<T, void>) {
+        return std::strong_ordering::equal;
+    }
+
+    return Underlying_ <=> rhs.Underlying_;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 
 template <class T>
@@ -117,13 +143,22 @@ struct hash<NYT::TStrongTypedef<T, TTag>>
 
 ////////////////////////////////////////////////////////////////////////////////
 
-template <class T>
-struct THash;
-
 template <class T, class TTag>
 struct THash<NYT::TStrongTypedef<T, TTag>>
-    : public std::hash<NYT::TStrongTypedef<T, TTag>>
-{ };
+{
+    size_t operator()(const NYT::TStrongTypedef<T, TTag>& value) const
+    {
+        static constexpr bool IsTHashable = requires (T val) {
+            { THash<T>()(val) } -> std::same_as<size_t>;
+        };
+
+        if constexpr (IsTHashable) {
+            return THash<T>()(value.Underlying());
+        } else {
+            return std::hash<T>()(value.Underlying());
+        }
+    }
+};
 
 ////////////////////////////////////////////////////////////////////////////////
 
diff --git a/library/cpp/yt/misc/strong_typedef.h b/library/cpp/yt/misc/strong_typedef.h
index 545029db8d4..d42f9e1f74b 100644
--- a/library/cpp/yt/misc/strong_typedef.h
+++ b/library/cpp/yt/misc/strong_typedef.h
@@ -30,7 +30,11 @@ public:
     constexpr explicit operator const T&() const;
     constexpr explicit operator T&();
 
-    constexpr auto operator<=>(const TStrongTypedef& rhs) const = default;
+    constexpr bool operator==(const TStrongTypedef& rhs) const
+    noexcept(std::same_as<T, void> || noexcept(Underlying_ == rhs.Underlying_));
+
+    constexpr auto operator<=>(const TStrongTypedef& rhs) const
+    noexcept(std::same_as<T, void> || noexcept(Underlying_ <=> rhs.Underlying_));
 
     constexpr T& Underlying() &;
     constexpr const T& Underlying() const &;
-- 
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