[libcxx-commits] [libcxx] [libc++] Simplify __unwrap_iter a bit (PR #175153)

[Nikolas Klauser via libcxx-commits]

https://github.com/philnik777 created https://github.com/llvm/llvm-project/pull/175153

`__unwrap_iter` doesn't need to SFINAE away, so we can just check inside the function body whether an iterator is copy constructible. This reduces the overload set, improving compile times a bit.


>From 20f5b4e5e8096a63cfac754d2fdd5b48debab961 Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Fri, 9 Jan 2026 12:11:23 +0100
Subject: [PATCH] [libc++] Simplify __unwrap_iter a bit

---
 libcxx/include/__algorithm/unwrap_iter.h | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/libcxx/include/__algorithm/unwrap_iter.h b/libcxx/include/__algorithm/unwrap_iter.h
index b66a682e765fa..ea862cd2f6f30 100644
--- a/libcxx/include/__algorithm/unwrap_iter.h
+++ b/libcxx/include/__algorithm/unwrap_iter.h
@@ -57,21 +57,19 @@ struct __unwrap_iter_impl<_Iter, true> {
   }
 };
 
-template <class _Iter,
-          class _Impl                                             = __unwrap_iter_impl<_Iter>,
-          __enable_if_t<is_copy_constructible<_Iter>::value, int> = 0>
+template <class _Iter, class _Impl = __unwrap_iter_impl<_Iter> >
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 decltype(_Impl::__unwrap(std::declval<_Iter>()))
 __unwrap_iter(_Iter __i) _NOEXCEPT {
-  return _Impl::__unwrap(__i);
-}
-
 // Allow input_iterators to be passed to __unwrap_iter (but not __rewrap_iter)
 #if _LIBCPP_STD_VER >= 20
-template <class _Iter, __enable_if_t<!is_copy_constructible<_Iter>::value, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI constexpr _Iter __unwrap_iter(_Iter __i) noexcept {
-  return __i;
-}
+  if constexpr (!is_copy_constructible_v<_Iter>) {
+    return __i;
+  } else
 #endif
+  {
+    return _Impl::__unwrap(__i);
+  }
+}
 
 template <class _OrigIter, class _Iter, class _Impl = __unwrap_iter_impl<_OrigIter> >
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _OrigIter __rewrap_iter(_OrigIter __orig_iter, _Iter __iter) _NOEXCEPT {