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[libc++] Fix random_shuffle in __cxx03/__algorithm/shuffle.h #155915

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[libc++] Fix random_shuffle in __cxx03/__algorithm/shuffle.h #155915

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zibi2
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@zibi2 zibi2 commented Aug 28, 2025

Before the change a declaration in question was like the following:

template <class _RandomAccessIterator, class _RandomNumberGenerator>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_DEPRECATED_IN_CXX14 void
random_shuffle(_RandomAccessIterator __first,
               _RandomAccessIterator __last,
#  ifndef _LIBCPP_CXX03_LANG
               _RandomNumberGenerator&& __rand)
#  else
               _RandomNumberGenerator& __rand)
#  endif

The frozen cxx03 header should use reference for the 3rd parameter of random_shuffle() template function.

@zibi2 zibi2 self-assigned this Aug 28, 2025
@zibi2 zibi2 requested a review from a team as a code owner August 28, 2025 20:19
@llvmbot llvmbot added the libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi. label Aug 28, 2025
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llvmbot commented Aug 28, 2025

@llvm/pr-subscribers-libcxx

Author: Zibi Sarbinowski (zibi2)

Changes

Before the change a declaration in question was like the following:

template &lt;class _RandomAccessIterator, class _RandomNumberGenerator&gt;
_LIBCPP_HIDE_FROM_ABI _LIBCPP_DEPRECATED_IN_CXX14 void
random_shuffle(_RandomAccessIterator __first,
               _RandomAccessIterator __last,
#  ifndef _LIBCPP_CXX03_LANG
               _RandomNumberGenerator&amp;&amp; __rand)
#  else
               _RandomNumberGenerator&amp; __rand)
#  endif

The frozen cxx03 header should use reference for the 3rd parameter of random_shuffle() template function.

Full diff: https://github.com/llvm/llvm-project/pull/155915.diff

1 Files Affected:

  • (modified) libcxx/include/__cxx03/__algorithm/shuffle.h (+1-1)
diff --git a/libcxx/include/__cxx03/__algorithm/shuffle.h b/libcxx/include/__cxx03/__algorithm/shuffle.h
index fee7028ae22ac..24cd71c71378b 100644
--- a/libcxx/include/__cxx03/__algorithm/shuffle.h
+++ b/libcxx/include/__cxx03/__algorithm/shuffle.h
@@ -109,7 +109,7 @@ _LIBCPP_HIDE_FROM_ABI void random_shuffle(_RandomAccessIterator __first, _Random
 
 template <class _RandomAccessIterator, class _RandomNumberGenerator>
 _LIBCPP_HIDE_FROM_ABI void
-random_shuffle(_RandomAccessIterator __first, _RandomAccessIterator __last, _RandomNumberGenerator&& __rand) {
+random_shuffle(_RandomAccessIterator __first, _RandomAccessIterator __last, _RandomNumberGenerator& __rand) {
   typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
   difference_type __d = __last - __first;
   if (__d > 1) {

philnik777
philnik777 reviewed Aug 29, 2025
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Why does this matter?

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zibi2 commented Aug 29, 2025

Why does this matter?

Otherwise the following will fail to compile with -std=c++03:

#include <algorithm>
#include <vector>

typedef std::vector<int>::iterator Iter;
typedef std::iterator_traits<Iter>::difference_type Diff;
typedef Diff (*RandomNumberGenerator)(Diff);
void f(Iter a1 ,Iter a2 ,RandomNumberGenerator& a3 ){
 return std::random_shuffle<Iter,RandomNumberGenerator>  (a1, a2, a3);
}

Expected to compile clean but received the following:

r.C:8:11: error: no matching function for call to 'random_shuffle'
    8 |    return std::random_shuffle<Iter,RandomNumberGenerator>  (a1, a2, a3);
      |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...

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@abhina-sree abhina-sree Awaiting requested review from abhina-sree

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