[libcxx-commits] [libcxx] [libc++] Implement LWG2991: variant copy constructor missing noexcept(see below) (PR #230241)

[A. Jiang via libcxx-commits]

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@@ -52,6 +52,16 @@ struct NTCopy {
 static_assert(!std::is_trivially_copy_constructible<NTCopy>::value, "");
 static_assert(std::is_copy_constructible<NTCopy>::value, "");
 
+struct NoThrowNTCopy {
+  constexpr NoThrowNTCopy(int v) : value(v) {}
+  NoThrowNTCopy(const NoThrowNTCopy& that) noexcept : value(that.value) {}
+  NoThrowNTCopy(NoThrowNTCopy&&) = delete;
+  int value;
+};
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frederick-vs-ja wrote:

It seems that we don't even (odr-) use the copy ctor, so we don't need it to be defined. The data member and the move ctor seem irrelavent.

```suggestion
struct NoThrowNTCopy {
  NoThrowNTCopy(const NoThrowNTCopy&) noexcept;
};
```

https://github.com/llvm/llvm-project/pull/230241