On Sat, 21 Sep 2024, Giuseppe D'Angelo wrote:
> On 31/07/2024 00:19, Jonathan Wakely wrote:
> > One more thing that I missed last time, sorry:
> >
> > +#if __glibcxx_string_view >= 202403L
> > + // const string & + string_view
> > + template<typename _CharT, typename _Traits, typename _Alloc>
> > + _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
> > + inline basic_string<_CharT, _Traits, _Alloc>
> > + operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
> > + __type_identity_t<basic_string_view<_CharT, _Traits>> __rhs)
> >
> > Since this is a C++26 feature, we can use [[nodiscard]] and constexpr
> > unconditionally, so it can be simply:
> >
> > + template<typename _CharT, typename _Traits, typename _Alloc>
> > + [[nodiscard]]
> > + constexpr basic_string<_CharT, _Traits, _Alloc>
> >
> > i.e. use [[nodiscard]] not the NODISCARD macro, and constexpr instead
> > of the CONSTEXPR macro and the inline keyword.
>
> Here's a rebased patch that also includes these changes.
>
> Thank you,
>
> --
> Giuseppe D'Angelo
>
> Subject: [PATCH] libstdc++: implement concatenation of strings and
> string_views
>
> This adds support for P2591R5, merged for C++26.
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/basic_string.h: Implement the four operator+
> overloads between basic_string and (types convertible to)
> basic_string_view.
> * include/bits/version.def: Bump the feature-testing macro.
> * include/bits/version.h: Regenerate.
> *
> testsuite/21_strings/basic_string/operators/char/op_plus_fspath_neg.cc: New
> test.
> *
> testsuite/21_strings/basic_string/operators/char/op_plus_string_view.cc: New
> test.
> *
> testsuite/21_strings/basic_string/operators/char/op_plus_string_view_compat.cc:
> New test.
>
> Signed-off-by: Giuseppe D'Angelo <giuseppe.dang...@kdab.com>
> ---
> libstdc++-v3/include/bits/basic_string.h | 48 +++++
> libstdc++-v3/include/bits/version.def | 5 +
> libstdc++-v3/include/bits/version.h | 7 +-
> .../operators/char/op_plus_fspath_neg.cc | 13 ++
> .../operators/char/op_plus_string_view.cc | 169 ++++++++++++++++++
> .../char/op_plus_string_view_compat.cc | 63 +++++++
> 6 files changed, 304 insertions(+), 1 deletion(-)
> create mode 100644
> libstdc++-v3/testsuite/21_strings/basic_string/operators/char/op_plus_fspath_neg.cc
> create mode 100644
> libstdc++-v3/testsuite/21_strings/basic_string/operators/char/op_plus_string_view.cc
> create mode 100644
> libstdc++-v3/testsuite/21_strings/basic_string/operators/char/op_plus_string_view_compat.cc
>
> diff --git a/libstdc++-v3/include/bits/basic_string.h
> b/libstdc++-v3/include/bits/basic_string.h
> index 120c0bc9a17..7cb2193230c 100644
> --- a/libstdc++-v3/include/bits/basic_string.h
> +++ b/libstdc++-v3/include/bits/basic_string.h
> @@ -3745,6 +3745,54 @@ _GLIBCXX_END_NAMESPACE_CXX11
> { return std::move(__lhs.append(1, __rhs)); }
> #endif
>
> +#if __glibcxx_string_view >= 202403L
> + // const string & + string_view
> + template<typename _CharT, typename _Traits, typename _Alloc>
> + [[nodiscard]]
> + constexpr inline basic_string<_CharT, _Traits, _Alloc>
Redundant 'inline's
> + operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
> + type_identity_t<basic_string_view<_CharT, _Traits>> __rhs)
> + {
> + typedef basic_string<_CharT, _Traits, _Alloc> _Str;
These typedefs might as well be usings instead
Besides that LGTM!
> + return std::__str_concat<_Str>(__lhs.data(), __lhs.size(),
> + __rhs.data(), __rhs.size(),
> + __lhs.get_allocator());
> + }
> +
> + // string && + string_view
> + template<typename _CharT, typename _Traits, typename _Alloc>
> + [[nodiscard]]
> + constexpr inline basic_string<_CharT, _Traits, _Alloc>
> + operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
> + type_identity_t<basic_string_view<_CharT, _Traits>> __rhs)
> + {
> + return std::move(__lhs.append(__rhs));
> + }
> +
> + // string_view + const string &
> + template<typename _CharT, typename _Traits, typename _Alloc>
> + [[nodiscard]]
> + constexpr inline basic_string<_CharT, _Traits, _Alloc>
> + operator+(type_identity_t<basic_string_view<_CharT, _Traits>> __lhs,
> + const basic_string<_CharT, _Traits, _Alloc>& __rhs)
> + {
> + typedef basic_string<_CharT, _Traits, _Alloc> _Str;
> + return std::__str_concat<_Str>(__lhs.data(), __lhs.size(),
> + __rhs.data(), __rhs.size(),
> + __rhs.get_allocator());
> + }
> +
> + // string_view + string &&
> + template<typename _CharT, typename _Traits, typename _Alloc>
> + [[nodiscard]]
> + constexpr inline basic_string<_CharT, _Traits, _Alloc>
> + operator+(type_identity_t<basic_string_view<_CharT, _Traits>> __lhs,
> + basic_string<_CharT, _Traits, _Alloc>&& __rhs)
> +
> + return std::move(__rhs.insert(0, __lhs));
> + }
> +#endif
> +
> // operator ==
> /**
> * @brief Test equivalence of two strings.
> diff --git a/libstdc++-v3/include/bits/version.def
> b/libstdc++-v3/include/bits/version.def
> index 23478523e0a..d1505c1a0ac 100644
> --- a/libstdc++-v3/include/bits/version.def
> +++ b/libstdc++-v3/include/bits/version.def
> @@ -698,6 +698,11 @@ ftms = {
>
> ftms = {
> name = string_view;
> + values = {
> + v = 202403;
> + cxxmin = 26;
> + hosted = yes;
> + };
> values = {
> v = 201803;
> cxxmin = 17;
> diff --git a/libstdc++-v3/include/bits/version.h
> b/libstdc++-v3/include/bits/version.h
> index 0fac749d91e..063ce695bef 100644
> --- a/libstdc++-v3/include/bits/version.h
> +++ b/libstdc++-v3/include/bits/version.h
> @@ -774,7 +774,12 @@
> #undef __glibcxx_want_shared_ptr_weak_type
>
> #if !defined(__cpp_lib_string_view)
> -# if (__cplusplus >= 201703L) && _GLIBCXX_HOSTED
> +# if (__cplusplus > 202302L) && _GLIBCXX_HOSTED
> +# define __glibcxx_string_view 202403L
> +# if defined(__glibcxx_want_all) || defined(__glibcxx_want_string_view)
> +# define __cpp_lib_string_view 202403L
> +# endif
> +# elif (__cplusplus >= 201703L) && _GLIBCXX_HOSTED
> # define __glibcxx_string_view 201803L
> # if defined(__glibcxx_want_all) || defined(__glibcxx_want_string_view)
> # define __cpp_lib_string_view 201803L
> diff --git
> a/libstdc++-v3/testsuite/21_strings/basic_string/operators/char/op_plus_fspath_neg.cc
>
> b/libstdc++-v3/testsuite/21_strings/basic_string/operators/char/op_plus_fspath_neg.cc
> new file mode 100644
> index 00000000000..bf1e09ada1e
> --- /dev/null
> +++
> b/libstdc++-v3/testsuite/21_strings/basic_string/operators/char/op_plus_fspath_neg.cc
> @@ -0,0 +1,13 @@
> +// { dg-do compile { target c++17 } }
> +
> +#include <filesystem>
> +#include <string>
> +
> +int main()
> +{
> + std::filesystem::path p = "/var/log/";
> + std::string s = "file";
> + // Concatenation of strings and string views (P2591R5)
> + // should not make this possible:
> + p + s; // { dg-error "no match for" "operator+(string,string_view) should
> not make this possible" }
> +}
> diff --git
> a/libstdc++-v3/testsuite/21_strings/basic_string/operators/char/op_plus_string_view.cc
>
> b/libstdc++-v3/testsuite/21_strings/basic_string/operators/char/op_plus_string_view.cc
> new file mode 100644
> index 00000000000..364d5bd5aba
> --- /dev/null
> +++
> b/libstdc++-v3/testsuite/21_strings/basic_string/operators/char/op_plus_string_view.cc
> @@ -0,0 +1,169 @@
> +// { dg-do run { target c++26 } }
> +
> +#include <string>
> +#include <type_traits>
> +#include <utility>
> +
> +#include <testsuite_hooks.h>
> +
> +#if !defined(__cpp_lib_string_view) || __cpp_lib_string_view < 202403L
> +#error "__cpp_lib_string_view should have been defined to 202403L or more"
> +#endif
> +
> +static_assert(std::is_same_v<decltype(std::declval<std::string>() +
> std::declval<std::string_view>()), std::string>);
> +static_assert(std::is_same_v<decltype(std::declval<std::string &>() +
> std::declval<std::string_view>()), std::string>);
> +static_assert(std::is_same_v<decltype(std::declval<std::string_view>() +
> std::declval<std::string>()), std::string>);
> +static_assert(std::is_same_v<decltype(std::declval<std::string_view>() +
> std::declval<std::string &>()), std::string>);
> +
> +struct convertible_to_string_view1
> +{
> + constexpr operator std::string_view() const { return "convertible_to_sv1";
> }
> +};
> +
> +struct convertible_to_string_view2
> +{
> + constexpr operator std::string_view() { return "convertible_to_sv2";
> }
> +};
> +
> +struct convertible_to_string_view3
> +{
> + constexpr operator std::string_view() { return "convertible_to_sv3
> non_const"; }
> + constexpr operator std::string_view() const { return "convertible_to_sv3
> const"; }
> +};
> +
> +struct convertible_to_string_view_and_char_star
> +{
> + constexpr operator std::string_view() const { return
> "convertible_to_sv_and_charstar1"; }
> + constexpr operator const char *() const { return
> "convertible_to_sv_and_charstar2"; }
> +};
> +
> +struct convertible_to_lots
> +{
> + constexpr operator std::string_view() const { return
> "convertible_to_lots1"; }
> + constexpr operator const char *() const { return "convertible_to_lots2"; }
> + constexpr operator std::string() const { return "convertible_to_lots3"; }
> +};
> +
> +using namespace std::literals;
> +static_assert( "costa "s + "marbella"sv == "costa marbella"s );
> +static_assert( "costa "sv + "marbella"s == "costa marbella"s );
> +static_assert( "costa "s + convertible_to_string_view1{} == "costa
> convertible_to_sv1"s );
> +static_assert( "costa "s + convertible_to_string_view2{} == "costa
> convertible_to_sv2"s );
> +static_assert( "costa "s + convertible_to_string_view3{} == "costa
> convertible_to_sv3 non_const"s );
> +static_assert( "costa "s + convertible_to_string_view_and_char_star{} ==
> "costa convertible_to_sv_and_charstar1"s );
> +static_assert( "costa "s + convertible_to_lots{} == "costa
> convertible_to_lots1"s );
> +
> +void
> +test01()
> +{
> + std::string str_0("costa ");
> + std::string str_1("marbella");
> +
> + std::string tmp;
> +
> + std::string_view str_0_view = str_0;
> + std::string_view str_1_view = str_1;
> +
> +
> + // string + string_view
> + VERIFY( (str_0 + str_1_view) == "costa marbella" );
> + VERIFY( (str_0 + std::as_const(str_1_view)) == "costa marbella" );
> + VERIFY( (str_0 + std::string_view(str_1)) == "costa marbella" );
> + VERIFY( (str_0_view + str_1) == "costa marbella" );
> + VERIFY( (std::as_const(str_0_view) + str_1) == "costa marbella" );
> + VERIFY( (std::string_view(str_0) + str_1) == "costa marbella" );
> + tmp = str_0;
> + VERIFY( (std::move(tmp) + str_1_view) == "costa marbella" );
> + tmp = str_1;
> + VERIFY( (str_0_view + std::move(tmp)) == "costa marbella" );
> +
> +
> + // convertible to string_view
> + convertible_to_string_view1 conv_string_view1;
> + VERIFY( (str_0 + conv_string_view1) == "costa convertible_to_sv1" );
> + VERIFY( (str_0 + std::as_const(conv_string_view1)) == "costa
> convertible_to_sv1" );
> + VERIFY( (std::as_const(str_0) + conv_string_view1) == "costa
> convertible_to_sv1" );
> + VERIFY( (std::as_const(str_0) + std::as_const(conv_string_view1)) ==
> "costa convertible_to_sv1" );
> +
> + tmp = str_0;
> + VERIFY( (std::move(tmp) + conv_string_view1) == "costa convertible_to_sv1"
> );
> + tmp = str_1;
> + VERIFY( (conv_string_view1 + std::move(tmp)) ==
> "convertible_to_sv1marbella" );
> +
> + VERIFY( (conv_string_view1 + str_1) == "convertible_to_sv1marbella" );
> + VERIFY( (conv_string_view1 + std::as_const(str_1)) ==
> "convertible_to_sv1marbella" );
> + VERIFY( (std::as_const(conv_string_view1) + str_1) ==
> "convertible_to_sv1marbella" );
> + VERIFY( (std::as_const(conv_string_view1) + std::as_const(str_1)) ==
> "convertible_to_sv1marbella" );
> +
> +
> + convertible_to_string_view2 conv_string_view2;
> + VERIFY( (str_0 + conv_string_view2) == "costa convertible_to_sv2" );
> + VERIFY( (std::as_const(str_0) + conv_string_view2) == "costa
> convertible_to_sv2" );
> + tmp = str_0;
> + VERIFY( (std::move(tmp) + conv_string_view2) == "costa convertible_to_sv2"
> );
> + tmp = str_1;
> + VERIFY( (conv_string_view2 + std::move(tmp)) ==
> "convertible_to_sv2marbella" );
> +
> +
> + convertible_to_string_view3 conv_string_view3;
> + VERIFY( (str_0 + conv_string_view3) == "costa convertible_to_sv3
> non_const" );
> + VERIFY( (str_0 + std::as_const(conv_string_view3)) == "costa
> convertible_to_sv3 const" );
> + VERIFY( (std::as_const(str_0) + conv_string_view3) == "costa
> convertible_to_sv3 non_const" );
> + VERIFY( (std::as_const(str_0) + std::as_const(conv_string_view3)) ==
> "costa convertible_to_sv3 const" );
> +
> + tmp = str_0;
> + VERIFY( (std::move(tmp) + conv_string_view3) == "costa convertible_to_sv3
> non_const" );
> + tmp = str_1;
> + VERIFY( (conv_string_view3 + std::move(tmp)) == "convertible_to_sv3
> non_constmarbella" );
> +
> + VERIFY( (conv_string_view3 + str_1) == "convertible_to_sv3
> non_constmarbella" );
> + VERIFY( (conv_string_view3 + std::as_const(str_1)) == "convertible_to_sv3
> non_constmarbella" );
> + VERIFY( (std::as_const(conv_string_view3) + str_1) == "convertible_to_sv3
> constmarbella" );
> + VERIFY( (std::as_const(conv_string_view3) + std::as_const(str_1)) ==
> "convertible_to_sv3 constmarbella" );
> +
> +
> + convertible_to_string_view_and_char_star conv_sv_cs;
> + VERIFY( (str_0 + conv_sv_cs) == "costa convertible_to_sv_and_charstar1" );
> + VERIFY( (conv_sv_cs + str_1) == "convertible_to_sv_and_charstar1marbella"
> );
> +
> +
> + convertible_to_lots conv_lots;
> + VERIFY( (str_0 + conv_lots) == "costa convertible_to_lots1" );
> + VERIFY( (conv_lots + str_1) == "convertible_to_lots1marbella" );
> +
> +
> + // Check that we're not regressing common cases
> + // string + string literal
> + VERIFY( (str_0 + "marbella") == "costa marbella" );
> + VERIFY( ("costa " + str_1) == "costa marbella" );
> +
> + tmp = str_0;
> + VERIFY( (std::move(tmp) + "marbella") == "costa marbella" );
> + tmp = str_1;
> + VERIFY( ("costa " + std::move(tmp)) == "costa marbella" );
> +
> +
> + // string + non-const char *
> + VERIFY( (str_0 + str_1.data()) == "costa marbella" );
> + VERIFY( (str_0.data() + str_1) == "costa marbella" );
> +
> + tmp = str_0;
> + VERIFY( (std::move(tmp) + str_1.data()) == "costa marbella" );
> + tmp = str_1;
> + VERIFY( (str_0.data() + std::move(tmp)) == "costa marbella" );
> +
> +
> + // string + const char *
> + VERIFY( (str_0 + std::as_const(str_1).data()) == "costa marbella" );
> + VERIFY( (std::as_const(str_0).data() + str_1) == "costa marbella" );
> +
> + tmp = str_0;
> + VERIFY( (std::move(tmp) + std::as_const(str_1).data()) == "costa marbella"
> );
> + tmp = str_1;
> + VERIFY( (std::as_const(str_0).data() + std::move(tmp)) == "costa marbella"
> );
> +}
> +
> +int main()
> +{
> + test01();
> +}
> diff --git
> a/libstdc++-v3/testsuite/21_strings/basic_string/operators/char/op_plus_string_view_compat.cc
>
> b/libstdc++-v3/testsuite/21_strings/basic_string/operators/char/op_plus_string_view_compat.cc
> new file mode 100644
> index 00000000000..d24f9fb2c1d
> --- /dev/null
> +++
> b/libstdc++-v3/testsuite/21_strings/basic_string/operators/char/op_plus_string_view_compat.cc
> @@ -0,0 +1,63 @@
> +// { dg-do compile { target c++17 } }
> +
> +#include <string>
> +#include <type_traits>
> +#include <utility>
> +
> +#include <testsuite_hooks.h>
> +
> +// "legacy" string view and operators
> +template <typename CharT>
> +struct basic_my_string_view
> +{
> + std::basic_string_view<CharT> view;
> +};
> +
> +using my_string_view = basic_my_string_view<char>;
> +
> +template <class T>
> +struct my_type_identity { using type = T; };
> +template <class T>
> +using my_type_identity_t = typename my_type_identity<T>::type;
> +
> +template <typename CharT, typename T, typename A>
> +std::string operator+(const std::basic_string<CharT, T, A> &s,
> basic_my_string_view<CharT> msv)
> +{
> + std::string result = s;
> + result += msv.view;
> + result += " using my_string_view";
> + return result;
> +}
> +
> +template <typename CharT, typename T, typename A>
> +std::string operator+(const std::basic_string<CharT, T, A> &s,
> my_type_identity_t<basic_my_string_view<CharT>> msv)
> +{
> + std::string result = s;
> + result += msv.view;
> + result += " using my_string_view";
> + return result;
> +}
> +
> +
> +struct buffer
> +{
> + std::string buf;
> +
> + // "legacy"
> + operator my_string_view() const { return my_string_view{buf}; }
> + // "modern"
> + operator std::string_view() const { return std::string_view{buf}; }
> +};
> +
> +int
> +main()
> +{
> + std::string s = "costa ";
> + buffer b{"marbella"};
> +
> + // This should be ambiguous in C++26 due to new operator+ overloads
> + // between std::string and objects convertible to std::string_view
> + // (P2591R5)
> + std::string result = s + b; // { dg-error "ambiguous"
> "operator+(string,string_view) should make this ambiguous" { target c++26 } }
> + VERIFY( result == "costa marbella using my_string_view" );
> +}
> --
> 2.34.1
