Re: [PATCH] libstdc++: Support maps deduction from_range of tuples.

Jonathan Wakely Wed, 26 Mar 2025 06:36:42 -0700

On 19/03/25 12:08 +0100, Tomasz Kamiński wrote:

This implements part of LWG2713 that enables deduction for maps types


LWG 4223 not 2713

(map, unordered_map, flat_map and non-unique equivalent) from
(from_range, rg, ...) arguments, where rg is range of tuple
and other pair-like.

libstdc++-v3/ChangeLog:

        * include/bits/ranges_base.h (__detail::__range_key_type):
        Replace RV::first_type with tuple_element_t<0, RV>.
        (__detail::__range_mapped_type) Replace RV::second_type
        with tuple_element_t<1, RV>.
        * testsuite/23_containers/flat_map/1.cc: New tests.
        * testsuite/23_containers/flat_multimap/1.cc: New tests.
        * testsuite/23_containers/map/cons/from_range.cc: New tests.
        * testsuite/23_containers/multimap/cons/from_range.cc: New tests.
        * testsuite/23_containers/unordered_map/cons/from_range.cc: New tests.
        * testsuite/23_containers/unordered_multimap/cons/from_range.cc:
        New tests.
---
This implements non-controvesial part of LWG2713, which provides
parity between iterator pair and from_range cosntructors.
Testing on x86_64-linux (*map* tests passed).
OK for trunk when test finishes?

libstdc++-v3/include/bits/ranges_base.h       |  8 ++-
.../testsuite/23_containers/flat_map/1.cc     | 61 +++++++++++++++++
.../23_containers/flat_multimap/1.cc          | 65 +++++++++++++++++++
.../23_containers/map/cons/from_range.cc      |  8 ++-
.../23_containers/multimap/cons/from_range.cc |  8 ++-
.../unordered_map/cons/from_range.cc          |  8 ++-
.../unordered_multimap/cons/from_range.cc     | 12 +++-
7 files changed, 156 insertions(+), 14 deletions(-)

diff --git a/libstdc++-v3/include/bits/ranges_base.h 
b/libstdc++-v3/include/bits/ranges_base.h
index c9687c256e9..7d5aee9c430 100644
--- a/libstdc++-v3/include/bits/ranges_base.h
+++ b/libstdc++-v3/include/bits/ranges_base.h
@@ -41,6 +41,10 @@
#include <bits/max_size_type.h>
#include <bits/version.h>

+#if __glibcxx_ranges_to_container // C++ >= 23
+# include <bits/utility.h> // for tuple_element_t
+#endif
+
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wpedantic" // __int128

@@ -1095,11 +1099,11 @@ namespace __detail


I think we should have a _GLIBCXX_RESOLVE_LIB_DEFECTS comment here, as
this changes something that was in the published C++23 standard. (We
only need one comment, since __range_mapped_type is right next to it.)

OK with that comment added, and the issue number in the commit message
fixed.

  template<ranges::input_range _Range>
    using __range_key_type
-      = remove_const_t<typename ranges::range_value_t<_Range>::first_type>;
+      = remove_const_t<tuple_element_t<0, ranges::range_value_t<_Range>>>;

  template<ranges::input_range _Range>
    using __range_mapped_type
-      = typename ranges::range_value_t<_Range>::second_type;
+      = tuple_element_t<1, ranges::range_value_t<_Range>>;

  // The allocator's value_type for map-like containers.
  template<ranges::input_range _Range>
diff --git a/libstdc++-v3/testsuite/23_containers/flat_map/1.cc 
b/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
index 00254dc2ee6..4e5ac9b62b7 100644
--- a/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
+++ b/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
@@ -11,6 +11,67 @@
#include <vector>
#include <testsuite_allocator.h>
#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+#include <tuple>
+
+struct Gt {
+  template<typename T, typename U>
+  bool operator()(T const& l, U const & r) const
+  { return l > r; }
+};
+
+void
+test_deduction_guide()
+{
+  __gnu_test::test_input_range<std::pair<long, float>> r(0, 0);
+  std::flat_map it1(std::from_range, r);
+  static_assert(std::is_same_v<decltype(it1), std::flat_map<long, float>>);
+  std::flat_map fr1(std::from_range, r);
+  static_assert(std::is_same_v<decltype(fr1), std::flat_map<long, float>>);
+
+  Gt cmp;
+  std::flat_map it2(r.begin(), r.begin(), cmp);
+  static_assert(std::is_same_v<decltype(it2), std::flat_map<long, float, Gt>>);
+  std::flat_map fr2(std::from_range, r, cmp);
+  static_assert(std::is_same_v<decltype(fr2), std::flat_map<long, float, Gt>>);
+
+  using Alloc = __gnu_test::SimpleAllocator<std::pair<const long, float>>;
+  Alloc alloc;
+  // No matching deduction guide
+  // std::flat_map it3(r.begin(), r.begin(), alloc);
+  std::flat_map fr3(std::from_range, r, alloc);
+  static_assert(std::is_same_v<
+     decltype(fr3),
+     std::flat_map<long, float, std::less<long>,
+                  std::vector<long, __gnu_test::SimpleAllocator<long>>,
+                  std::vector<float, __gnu_test::SimpleAllocator<float>>>>);
+
+  // No matching deduction guide
+  // std::flat_map it4(r.begin(), r.begin(), cmp, alloc);
+  std::flat_map fr4(std::from_range, r, cmp, alloc);
+  static_assert(std::is_same_v<
+     decltype(fr4),
+     std::flat_map<long, float, Gt,
+                  std::vector<long, __gnu_test::SimpleAllocator<long>>,
+                  std::vector<float, __gnu_test::SimpleAllocator<float>>>>);
+
+  // LWG4223: deduces flat_map<long, float const>, which in turn instantiates
+  // std::vector<cosnt float> that is ill-formed.
+  // __gnu_test::test_input_range<std::pair<const long, const float>> r2(0, 0);
+  // std::flat_map it5(r2.begin(), r2.begin());
+  // std::flat_map fr5(std::from_range, r2);
+
+  // LWG4223: deduces flat_map<const long&, float&>
+  //__gnu_test::test_input_range<std::pair<const long&, float&>> r3(0, 0);
+  // std::flat_map it6(r3.begin(), r3.begin());
+  // std::flat_map fr6(std::from_range, r3);
+
+  __gnu_test::test_input_range<std::tuple<long, float>> r4(0, 0);
+  std::flat_map it7(r4.begin(), r4.begin());
+  static_assert(std::is_same_v<decltype(it7), std::flat_map<long, float>>);
+  std::flat_map fr7(std::from_range, r4);
+  static_assert(std::is_same_v<decltype(fr7), std::flat_map<long, float>>);
+}

template<template<typename> class KeyContainer, template<typename> class 
MappedContainer>
void
diff --git a/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc 
b/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
index 38650a81bcf..62bda65d79f 100644
--- a/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
+++ b/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
@@ -5,6 +5,71 @@
#include <vector>
#include <testsuite_allocator.h>
#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+#include <tuple>
+
+struct Gt {
+  template<typename T, typename U>
+  bool operator()(T const& l, U const & r) const
+  { return l > r; }
+};
+
+void
+test_deduction_guide()
+{
+  __gnu_test::test_input_range<std::pair<long, float>> r(0, 0);
+  std::flat_multimap it1(std::from_range, r);
+  static_assert(std::is_same_v<decltype(it1), std::flat_multimap<long, 
float>>);
+  std::flat_multimap fr1(std::from_range, r);
+  static_assert(std::is_same_v<decltype(fr1), std::flat_multimap<long, 
float>>);
+
+  Gt cmp;
+  std::flat_multimap it2(r.begin(), r.begin(), cmp);
+  static_assert(std::is_same_v<
+    decltype(it2),
+    std::flat_multimap<long, float, Gt>>);
+  std::flat_multimap fr2(std::from_range, r, cmp);
+  static_assert(std::is_same_v<
+    decltype(fr2),
+    std::flat_multimap<long, float, Gt>>);
+
+  using Alloc = __gnu_test::SimpleAllocator<std::pair<const long, float>>;
+  Alloc alloc;
+  // No matching deduction guide
+  // std::flat_multimap it3(r.begin(), r.begin(), alloc);
+  std::flat_multimap fr3(std::from_range, r, alloc);
+  static_assert(std::is_same_v<
+     decltype(fr3),
+     std::flat_multimap<long, float, std::less<long>,
+                  std::vector<long, __gnu_test::SimpleAllocator<long>>,
+                  std::vector<float, __gnu_test::SimpleAllocator<float>>>>);
+
+  // No matching deduction guide
+  // std::flat_multimap it4(r.begin(), r.begin(), cmp, alloc);
+  std::flat_multimap fr4(std::from_range, r, cmp, alloc);
+  static_assert(std::is_same_v<
+     decltype(fr4),
+     std::flat_multimap<long, float, Gt,
+                  std::vector<long, __gnu_test::SimpleAllocator<long>>,
+                  std::vector<float, __gnu_test::SimpleAllocator<float>>>>);
+
+  // LWG4223: deduces flat_multimap<long, float const>, which in turn 
instantiates
+  // std::vector<cosnt float> that is ill-formed.
+  // __gnu_test::test_input_range<std::pair<const long, const float>> r2(0, 0);
+  // std::flat_multimap it5(r2.begin(), r2.begin());
+  // std::flat_multimap fr5(std::from_range, r2);
+
+  // LWG4223: deduces flat_multimap<const long&, float&>
+  //__gnu_test::test_input_range<std::pair<const long&, float&>> r3(0, 0);
+  // std::flat_multimap it6(r3.begin(), r3.begin());
+  // std::flat_multimap fr6(std::from_range, r3);
+
+  __gnu_test::test_input_range<std::tuple<long, float>> r4(0, 0);
+  std::flat_multimap it7(r4.begin(), r4.begin());
+  static_assert(std::is_same_v<decltype(it7), std::flat_multimap<long, 
float>>);
+  std::flat_multimap fr7(std::from_range, r4);
+  static_assert(std::is_same_v<decltype(fr7), std::flat_multimap<long, 
float>>);
+}

template<template<typename> class KeyContainer, template<typename> class 
MappedContainer>
void
diff --git a/libstdc++-v3/testsuite/23_containers/map/cons/from_range.cc 
b/libstdc++-v3/testsuite/23_containers/map/cons/from_range.cc
index 01e426fde3d..c740471f2da 100644
--- a/libstdc++-v3/testsuite/23_containers/map/cons/from_range.cc
+++ b/libstdc++-v3/testsuite/23_containers/map/cons/from_range.cc
@@ -44,9 +44,11 @@ test_deduction_guide()
  //__gnu_test::test_input_range<std::pair<const long&, float&>> r3(0, 0);
  // std::map m6(std::from_range, r3);

-  // LWG4223: no deduction guide
-  // __gnu_test::test_input_range<std::tuple<long, float>> r4(0, 0);
-  // std::map m7(std::from_range, r4);
+  __gnu_test::test_input_range<std::tuple<long, float>> r4(0, 0);
+  std::map m7(std::from_range, r4);
+  static_assert(std::is_same_v<decltype(m7), std::map<long, float>>);
+  std::map it7(r4.begin(), r4.begin());
+  static_assert(std::is_same_v<decltype(it7), std::map<long, float>>);
}

template<typename T, typename U>
diff --git a/libstdc++-v3/testsuite/23_containers/multimap/cons/from_range.cc 
b/libstdc++-v3/testsuite/23_containers/multimap/cons/from_range.cc
index e0052e499ca..3e456f566cc 100644
--- a/libstdc++-v3/testsuite/23_containers/multimap/cons/from_range.cc
+++ b/libstdc++-v3/testsuite/23_containers/multimap/cons/from_range.cc
@@ -44,9 +44,11 @@ test_deduction_guide()
  //__gnu_test::test_input_range<std::pair<const long&, float&>> r3(0, 0);
  // std::multimap m6(std::from_range, r3);

-  // LWG4223: no deduction guide
-  // __gnu_test::test_input_range<std::tuple<long, float>> r4(0, 0);
-  // std::multimap m7(std::from_range, r4);
+  __gnu_test::test_input_range<std::tuple<long, float>> r4(0, 0);
+  std::multimap m7(std::from_range, r4);
+  static_assert(std::is_same_v<decltype(m7), std::multimap<long, float>>);
+  std::multimap it7(r4.begin(), r4.begin());
+  static_assert(std::is_same_v<decltype(it7), std::multimap<long, float>>);
}

template<typename T, typename U>
diff --git 
a/libstdc++-v3/testsuite/23_containers/unordered_map/cons/from_range.cc 
b/libstdc++-v3/testsuite/23_containers/unordered_map/cons/from_range.cc
index b3cbb2e6062..a15bfaa48b3 100644
--- a/libstdc++-v3/testsuite/23_containers/unordered_map/cons/from_range.cc
+++ b/libstdc++-v3/testsuite/23_containers/unordered_map/cons/from_range.cc
@@ -82,9 +82,11 @@ test_deduction_guide()
  // __gnu_test::test_input_range<std::pair<const long&, float&>> r3(0, 0);
  // std::unordered_map m10(std::from_range, r3);

-  // LWG4223: no deduction guide
-  // __gnu_test::test_input_range<std::tuple<long, float>> r4(0, 0);
-  // std::unordered_map m11(std::from_range, r4);
+  __gnu_test::test_input_range<std::tuple<long, float>> r4(0, 0);
+  std::unordered_map m11(std::from_range, r4);
+  static_assert(std::is_same_v<decltype(m11), std::unordered_map<long, 
float>>);
+  std::unordered_map it11(r4.begin(), r4.begin());
+  static_assert(std::is_same_v<decltype(it11), std::unordered_map<long, 
float>>);
}

template<typename T, typename U>
diff --git 
a/libstdc++-v3/testsuite/23_containers/unordered_multimap/cons/from_range.cc 
b/libstdc++-v3/testsuite/23_containers/unordered_multimap/cons/from_range.cc
index 9273ef0d57a..416d9e08395 100644
--- a/libstdc++-v3/testsuite/23_containers/unordered_multimap/cons/from_range.cc
+++ b/libstdc++-v3/testsuite/23_containers/unordered_multimap/cons/from_range.cc
@@ -87,9 +87,15 @@ test_deduction_guide()
  // __gnu_test::test_input_range<std::pair<const long&, float&>> r3(0, 0);
  // std::unordered_multimap m10(std::from_range, r3);

-  // LWG4223: no deduction guide
-  // __gnu_test::test_input_range<std::tuple<long, float>> r4(0, 0);
-  // std::unordered_multimap m11(std::from_range, r4);
+  __gnu_test::test_input_range<std::tuple<long, float>> r4(0, 0);
+  std::unordered_multimap m11(std::from_range, r4);
+  static_assert(std::is_same_v<
+    decltype(m11),
+    std::unordered_multimap<long, float>>);
+  std::unordered_multimap it11(r4.begin(), r4.begin());
+  static_assert(std::is_same_v<
+    decltype(it11),
+    std::unordered_multimap<long, float>>);
}

template<typename T, typename U>
--
2.48.1

Re: [PATCH] libstdc++: Support maps deduction from_range of tuples.

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