From: Feng Jisen <J1senn@outlook.com>
To: "libstdc++@gcc.gnu.org" <libstdc++@gcc.gnu.org>,
"gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>
Subject: Remove redundant partial specialization in _Nth_type
Date: Sat, 28 Oct 2023 13:14:36 +0000 [thread overview]
Message-ID: <PN2P287MB04959F8A5240E7CC19930B2991A3A@PN2P287MB0495.INDP287.PROD.OUTLOOK.COM> (raw)
[-- Attachment #1.1: Type: text/plain, Size: 1927 bytes --]
This patch remove a redundant partial specialization in class _Nth_type.
For the original metafunction _Nth_type code,
# 0
template<typename _Tp0, typename... _Rest>
struct _Nth_type<0, _Tp0, _Rest...>
{ using type = _Tp0; };
# 1
template<typename _Tp0, typename _Tp1, typename... _Rest>
struct _Nth_type<0, _Tp0, _Tp1, _Rest...>
{ using type = _Tp0; };
# 2
template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest>
struct _Nth_type<0, _Tp0, _Tp1, _Tp2, _Rest...>
{ using type = _Tp0; };
# 3
template<size_t _Np, typename _Tp0, typename _Tp1, typename _Tp2,
typename... _Rest>
#if __cpp_concepts
requires (_Np >= 3)
#endif
struct _Nth_type<_Np, _Tp0, _Tp1, _Tp2, _Rest...>
: _Nth_type<_Np - 3, _Rest...>
{ };
we need partial specialization # 2 to deal with template argument <0, Tp0, Tp1, Tp2, ...>.
Because without concepts, both # 0 and # 3 is legal and there is no partial order relationship between them.
However, # 1 is redundant. For template argument <0, Tp0, Tp1>, #0 is instantiated and that's enough.
libstdc++-v3/ChangeLog:
* include/bits/utility.h:(_Nth_type) Remove redundant partial specialization.
diff --git a/libstdc++-v3/include/bits/utility.h b/libstdc++-v3/include/bits/utility.h
index bed94525642..8766dfbc15f 100644
--- a/libstdc++-v3/include/bits/utility.h
+++ b/libstdc++-v3/include/bits/utility.h
@@ -258,10 +258,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{ };
#if ! __cpp_concepts // Need additional specializations to avoid ambiguities.
- template<typename _Tp0, typename _Tp1, typename... _Rest>
- struct _Nth_type<0, _Tp0, _Tp1, _Rest...>
- { using type = _Tp0; };
-
template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest>
struct _Nth_type<0, _Tp0, _Tp1, _Tp2, _Rest...>
{ using type = _Tp0; };
--
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[-- Attachment #2: 0001-remove-redundant-partial-template-in-_Nth_type.patch --]
[-- Type: text/x-patch; name="0001-remove-redundant-partial-template-in-_Nth_type.patch", Size: 954 bytes --]
From 6443b75b1097ed3d1a691535a4c5e9e9a96a935a Mon Sep 17 00:00:00 2001
From: J1senn <J1senn@outlook.com>
Date: Sat, 28 Oct 2023 20:49:42 +0800
Subject: [PATCH] remove redundant partial template in _Nth_type
---
libstdc++-v3/include/bits/utility.h | 4 ----
1 file changed, 4 deletions(-)
diff --git a/libstdc++-v3/include/bits/utility.h b/libstdc++-v3/include/bits/utility.h
index bed94525642..8766dfbc15f 100644
--- a/libstdc++-v3/include/bits/utility.h
+++ b/libstdc++-v3/include/bits/utility.h
@@ -258,10 +258,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{ };
#if ! __cpp_concepts // Need additional specializations to avoid ambiguities.
- template<typename _Tp0, typename _Tp1, typename... _Rest>
- struct _Nth_type<0, _Tp0, _Tp1, _Rest...>
- { using type = _Tp0; };
-
template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest>
struct _Nth_type<0, _Tp0, _Tp1, _Tp2, _Rest...>
{ using type = _Tp0; };
--
2.42.0
next reply other threads:[~2023-10-28 13:14 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-28 13:14 Feng Jisen [this message]
2023-11-03 15:36 ` Patrick Palka
2023-11-04 8:45 ` Jonathan Wakely
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