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Different implementation of map and flat_map

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This commit is contained in:
Andrzej Krzemienski
2024-08-15 21:41:17 +02:00
parent e360de3da5
commit 411ead088d
2 changed files with 38 additions and 13 deletions
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7
include/boost/optional/detail/optional_reference_spec.hpp
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@@ -168,7 +168,8 @@ public:
bool has_value() const BOOST_NOEXCEPT { return ptr_ != 0; } bool has_value() const BOOST_NOEXCEPT { return ptr_ != 0; }
template <typename F> template <typename F>
auto map(F f) const -> optional<decltype(f(**this))> optional<typename optional_detail::result_of<F, reference_const_type>::type>
map(F f) const
{ {
if (this->has_value()) if (this->has_value())
return f(this->get()); return f(this->get());
@@ -177,8 +178,8 @@ public:
} }
template <typename F> template <typename F>
auto flat_map(F f) const -> optional<typename optional_detail::result_value_type<F, reference_const_type>::type>
optional<typename optional_detail::optional_value_type<decltype(f(**this))>::type> flat_map(F f) const
{ {
if (this->has_value()) if (this->has_value())
return f(get()); return f(get());

44
include/boost/optional/optional.hpp
View File

@@ -76,6 +76,23 @@ struct optional_value_type< ::boost::optional<U> >
template <typename T> template <typename T>
T declval(); T declval();
// implementing my own result_of so that it works for C++11 (std::result_of)
// and in C++20 (std::invoke_result).
template <typename F, typename Ref, typename Rslt = decltype(declval<F>()(declval<Ref>()))>
struct result_of
{
typedef Rslt type;
};
template <typename F, typename Ref, typename Rslt = typename optional_value_type<typename result_of<F, Ref>::type>::type>
struct result_value_type
{
typedef Rslt type;
};
// optional<typename optional_detail::optional_value_type<decltype(optional_detail::declval<F>()(optional_detail::declval<reference_type>()))>::type>
}} // namespace boost::optional_detail }} // namespace boost::optional_detail
namespace boost { namespace boost {
@@ -1396,7 +1413,7 @@ class optional
} }
template <typename F> template <typename F>
optional<decltype(optional_detail::declval<F>()(optional_detail::declval<reference_type>()))> map(F f) & optional<typename optional_detail::result_of<F, reference_type>::type> map(F f) &
{ {
if (this->has_value()) if (this->has_value())
return f(get()); return f(get());
@@ -1405,7 +1422,7 @@ class optional
} }
template <typename F> template <typename F>
optional<decltype(optional_detail::declval<F>()(optional_detail::declval<reference_const_type>()))> map(F f) const& optional<typename optional_detail::result_of<F, reference_const_type>::type> map(F f) const&
{ {
if (this->has_value()) if (this->has_value())
return f(get()); return f(get());
@@ -1414,7 +1431,7 @@ class optional
} }
template <typename F> template <typename F>
optional<decltype(optional_detail::declval<F>()(optional_detail::declval<reference_type_of_temporary_wrapper>()))> map(F f) && optional<typename optional_detail::result_of<F, reference_type_of_temporary_wrapper>::type> map(F f) &&
{ {
if (this->has_value()) if (this->has_value())
return f(boost::move(this->get())); return f(boost::move(this->get()));
@@ -1423,7 +1440,8 @@ class optional
} }
template <typename F> template <typename F>
optional<typename optional_detail::optional_value_type<decltype(optional_detail::declval<F>()(optional_detail::declval<reference_type>()))>::type> flat_map(F f) & optional<typename optional_detail::result_value_type<F, reference_type>::type>
flat_map(F f) &
{ {
if (this->has_value()) if (this->has_value())
return f(get()); return f(get());
@@ -1432,7 +1450,8 @@ class optional
} }
template <typename F> template <typename F>
optional<typename optional_detail::optional_value_type<decltype(optional_detail::declval<F>()(optional_detail::declval<reference_const_type>()))>::type>flat_map(F f) const& optional<typename optional_detail::result_value_type<F, reference_const_type>::type>
flat_map(F f) const&
{ {
if (this->has_value()) if (this->has_value())
return f(get()); return f(get());
@@ -1441,7 +1460,8 @@ class optional
} }
template <typename F> template <typename F>
optional<typename optional_detail::optional_value_type<decltype(optional_detail::declval<F>()(optional_detail::declval<reference_type_of_temporary_wrapper>()))>::type>flat_map(F f) && optional<typename optional_detail::result_value_type<F, reference_type_of_temporary_wrapper>::type>
flat_map(F f) &&
{ {
if (this->has_value()) if (this->has_value())
return f(boost::move(get())); return f(boost::move(get()));
@@ -1460,7 +1480,8 @@ class optional
} }
template <typename F> template <typename F>
optional<decltype(optional_detail::declval<F>()(optional_detail::declval<reference_type>()))> map(F f) optional<typename optional_detail::result_of<F, reference_type>::type>
map(F f)
{ {
if (this->has_value()) if (this->has_value())
return f(get()); return f(get());
@@ -1469,7 +1490,8 @@ class optional
} }
template <typename F> template <typename F>
optional<decltype(optional_detail::declval<F>()(optional_detail::declval<reference_const_type>()))> map(F f) const optional<typename optional_detail::result_of<F, reference_const_type>::type>
map(F f) const
{ {
if (this->has_value()) if (this->has_value())
return f(get()); return f(get());
@@ -1478,7 +1500,8 @@ class optional
} }
template <typename F> template <typename F>
optional<typename optional_detail::optional_value_type<decltype(optional_detail::declval<F>()(optional_detail::declval<reference_type>()))>::type> flat_map(F f) optional<typename optional_detail::result_value_type<F, reference_type>::type>
flat_map(F f)
{ {
if (this->has_value()) if (this->has_value())
return f(get()); return f(get());
@@ -1487,7 +1510,8 @@ class optional
} }
template <typename F> template <typename F>
optional<typename optional_detail::optional_value_type<decltype(optional_detail::declval<F>()(optional_detail::declval<reference_const_type>()))>::type> flat_map(F f) const optional<typename optional_detail::result_value_type<F, reference_const_type>::type>
flat_map(F f) const
{ {
if (this->has_value()) if (this->has_value())
return f(get()); return f(get());