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remove copying when invoking objects stored in sbo #24

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remove copying when invoking objects stored in sbo #24

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12 changes: 6 additions & 6 deletions include/boost/compat/move_only_function.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -247,7 +247,7 @@ bool is_nullary_arg( F f )
template<bool NoEx, class R, class ...Args>
struct mo_invoke_function_holder
{
static R invoke_function( storage s, Args&&... args) noexcept( NoEx )
static R invoke_function( storage const& s, Args&&... args) noexcept( NoEx )
{
auto f = reinterpret_cast<R(*)( Args... )>( s.pfn_ );
return compat::invoke_r<R>( f, std::forward<Args>( args )... );
Expand All @@ -257,7 +257,7 @@ struct mo_invoke_function_holder
template<ref_quals RQ, bool Const, bool NoEx, class F, class R, class ...Args>
struct mo_invoke_object_holder
{
static R invoke_object( storage s, Args&&... args ) noexcept( NoEx )
static R invoke_object( storage const& s, Args&&... args ) noexcept( NoEx )
{
using T = remove_reference_t<F>;
using cv_T = conditional_t<Const, add_const_t<T>, T>;
Expand All @@ -274,7 +274,7 @@ struct mo_invoke_object_holder
template<ref_quals RQ, bool Const, bool NoEx, class F, class R, class ...Args>
struct mo_invoke_local_holder
{
static R invoke_local( storage s, Args&&... args ) noexcept( NoEx )
static R invoke_local( storage const& s, Args&&... args ) noexcept( NoEx )
{
using T = remove_reference_t<F>;
using cv_T = conditional_t<Const, add_const_t<T>, T>;
Expand All @@ -285,7 +285,7 @@ struct mo_invoke_local_holder
>
>;

return compat::invoke_r<R>( static_cast<cv_ref_T>( *static_cast<cv_T*>( s.addr() ) ), std::forward<Args>( args )... );
return compat::invoke_r<R>( static_cast<cv_ref_T>( *static_cast<cv_T*>( const_cast<storage&>( s ).addr() ) ), std::forward<Args>( args )... );
}
};

Expand Down Expand Up @@ -485,9 +485,9 @@ struct move_only_function_base

detail::storage s_;
#if defined(__cpp_noexcept_function_type)
R ( *invoke_ )( detail::storage, Args&&... ) noexcept( NoEx ) = nullptr;
R ( *invoke_ )( detail::storage const&, Args&&... ) noexcept( NoEx ) = nullptr;
#else
R ( *invoke_ )( detail::storage, Args&&... ) = nullptr;
R ( *invoke_ )( detail::storage const&, Args&&... ) = nullptr;
#endif
void ( *manager_ )( op_type, detail::storage&, detail::storage* ) = &manage_empty;
};
Expand Down
36 changes: 35 additions & 1 deletion test/move_only_function_test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,8 @@
#include <boost/core/lightweight_test.hpp>
#include <boost/core/lightweight_test_trait.hpp>

#include <functional>
#include <array>
#include <cstdint>
#include <memory>
#include <type_traits>

Expand All @@ -25,6 +26,11 @@
# pragma clang diagnostic ignored "-Wself-move"
#endif

#ifdef _MSC_VER
#pragma warning(disable: 4789) // false buffer overrun warning in test_mutable_lambda()
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@pdimov pdimov Jan 18, 2026

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What is the buffer overrun warning?

#endif


using std::is_same;
using std::is_constructible;
using std::is_nothrow_constructible;
Expand Down Expand Up @@ -845,11 +851,39 @@ static void test_conv()
}
}

static void test_mutable_lambda()
{
{
// Within SBO limits.
int captured = 0;
move_only_function<int()> func = [captured]() mutable { return ++captured; };

BOOST_TEST_EQ( func(), 1 );
BOOST_TEST_EQ( func(), 2 );

move_only_function<int()> func2(std::move(func));
BOOST_TEST_EQ( func2(), 3 );
}

{
// Too large for SBO.
std::array<std::uint8_t, 256> captured = {{}};
move_only_function<int()> func = [captured]() mutable { return ++captured[0]; };

BOOST_TEST_EQ( func(), 1 );
BOOST_TEST_EQ( func(), 2 );

move_only_function<int()> func2(std::move(func));
BOOST_TEST_EQ( func2(), 3 );
}
}

int main()
{
test_call();
test_traits();
test_conv();
test_mutable_lambda();

return boost::report_errors();
}