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P0318R1 unwrap_ref_decay and unwrap_reference #2471

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Nov 26, 2018
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P0318R1 unwrap_ref_decay and unwrap_reference #2471

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P0318R1 unwrap_ref_decay and unwrap_reference
jensmaurer Nov 15, 2018
9232666
[pairs.spec,tuple.creation] Simplify description
jensmaurer Nov 17, 2018
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45 changes: 29 additions & 16 deletions source/utilities.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -852,16 +852,16 @@
\indexlibrary{\idxcode{make_pair}}%
\begin{itemdecl}
template<class T1, class T2>
constexpr pair<V1, V2> make_pair(T1&& x, T2&& y);
constexpr pair<unwrap_ref_decay_t<T1>, unwrap_ref_decay_t<T2>> make_pair(T1&& x, T2&& y);
\end{itemdecl}

\begin{itemdescr}
\pnum
\returns \tcode{pair<V1, V2>(std::forward<T1>(x), std::forward<T2>(y))},
where \tcode{V1} and \tcode{V2} are determined as follows: Let \tcode{Ui} be
\tcode{decay_t<Ti>} for each \tcode{Ti}. If \tcode{Ui} is a specialization
of \tcode{reference_wrapper}, then \tcode{Vi} is \tcode{Ui::type\&},
otherwise \tcode{Vi} is \tcode{Ui}.
\returns
\begin{codeblock}
pair<unwrap_ref_decay_t<T1>,
unwrap_ref_decay_t<T2>>(std::forward<T1>(x), std::forward<T2>(y))
\end{codeblock}
\end{itemdescr}

\pnum
Expand Down Expand Up @@ -999,7 +999,7 @@
inline constexpr @\unspec@ ignore;

template<class... TTypes>
constexpr tuple<VTypes...> make_tuple(TTypes&&...);
constexpr tuple<unwrap_ref_decay_t<TTypes>...> make_tuple(TTypes&&...);

template<class... TTypes>
constexpr tuple<TTypes&&...> forward_as_tuple(TTypes&&...) noexcept;
Expand Down Expand Up @@ -1610,18 +1610,12 @@
\indexlibrary{\idxcode{tuple}!\idxcode{make_tuple}}%
\begin{itemdecl}
template<class... TTypes>
constexpr tuple<VTypes...> make_tuple(TTypes&&... t);
constexpr tuple<unwrap_ref_decay_t<TTypes>...> make_tuple(TTypes&&... t);
\end{itemdecl}

\begin{itemdescr}
\pnum
The pack \tcode{VTypes} is defined as follows. Let \tcode{U}$_i$ be \tcode{decay_t<T$_i$>} for each
\tcode{T}$_i$ in \tcode{TTypes}. If \tcode{U}$_i$ is a specialization of
\tcode{reference_wrapper}, then \tcode{V}$_i$ in \tcode{VTypes} is \tcode{U$_i$::type\&},
otherwise \tcode{V}$_i$ is \tcode{U}$_i$.

\pnum
\returns \tcode{tuple<VTypes...>(std::forward<TTypes>(t)...)}.
\returns \tcode{tuple<unwrap_ref_decay_t<TTypes>...>(std::forward<TTypes>(t)...)}.

\pnum
\begin{example}
Expand Down Expand Up @@ -13033,6 +13027,8 @@
\rSec2[functional.syn]{Header \tcode{<functional>} synopsis}

\indexhdr{functional}%
\indexlibrary{\idxcode{unwrap_ref_decay}}%
\indexlibrary{\idxcode{unwrap_ref_decay_t}}%
\begin{codeblock}
namespace std {
// \ref{func.invoke}, invoke
Expand All @@ -13051,6 +13047,10 @@
template<class T> reference_wrapper<T> ref(reference_wrapper<T>) noexcept;
template<class T> reference_wrapper<const T> cref(reference_wrapper<T>) noexcept;

template<class T> struct unwrap_reference;
template<class T> struct unwrap_ref_decay : unwrap_reference<decay_t<T>> {};
template<class T> using unwrap_ref_decay_t = typename unwrap_ref_decay<T>::type;

// \ref{arithmetic.operations}, arithmetic operations
template<class T = void> struct plus;
template<class T = void> struct minus;
Expand Down Expand Up @@ -13407,7 +13407,6 @@
\pnum\returns The stored reference.
\end{itemdescr}


\rSec3[refwrap.invoke]{Invocation}

\indexlibrarymember{operator()}{reference_wrapper}%
Expand Down Expand Up @@ -13460,6 +13459,20 @@
\pnum\returns \tcode{cref(t.get())}.
\end{itemdescr}

\rSec3[refwrap.unwrapref]{Transformation type trait \tcode{unwrap_reference}}

\indexlibrary{\idxcode{unwrap_reference}}%
\begin{itemdecl}
template<class T>
struct unwrap_reference;
\end{itemdecl}

\pnum
If \tcode{T} is
a specialization \tcode{reference_wrapper<X>} for some type \tcode{X},
the member typedef \tcode{type} of \tcode{unwrap_reference<T>} is \tcode{X\&},
otherwise it is \tcode{T}.

\rSec2[arithmetic.operations]{Arithmetic operations}

\pnum
Expand Down