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Jun 16, 2021
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P1659R3 starts_with and ends_with #4674

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105 changes: 105 additions & 0 deletions source/algorithms.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -1131,6 +1131,36 @@
constexpr ForwardIterator
search(ForwardIterator first, ForwardIterator last, const Searcher& searcher);

namespace ranges {
// \ref{alg.starts.with}, starts with
template<@\libconcept{input_iterator}@ I1, @\libconcept{sentinel_for}@<I1> S1, @\libconcept{input_iterator}@ I2, @\libconcept{sentinel_for}@<I2> S2,
class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity>
requires @\libconcept{indirectly_comparable}@<I1, I2, Pred, Proj1, Proj2>
constexpr bool starts_with(I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = {},
Proj1 proj1 = {}, Proj2 proj2 = {});
template<@\libconcept{input_range}@ R1, @\libconcept{input_range}@ R2, class Pred = ranges::equal_to,
class Proj1 = identity, class Proj2 = identity>
requires @\libconcept{indirectly_comparable}@<iterator_t<R1>, iterator_t<R2>, Pred, Proj1, Proj2>
constexpr bool starts_with(R1&& r1, R2&& r2, Pred pred = {},
Proj1 proj1 = {}, Proj2 proj2 = {});

// \ref{alg.ends.with}, ends with
template<@\libconcept{input_iterator}@ I1, @\libconcept{sentinel_for}@<I1> S1, @\libconcept{input_iterator}@ I2, @\libconcept{sentinel_for}@<I2> S2,
class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity>
requires (@\libconcept{forward_iterator}@<I1> || @\libconcept{sized_sentinel_for}@<S1, I1>) &&
(@\libconcept{forward_iterator}@<I2> || @\libconcept{sized_sentinel_for}@<S2, I2>) &&
@\libconcept{indirectly_comparable}@<I1, I2, Pred, Proj1, Proj2>
constexpr bool ends_with(I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = {},
Proj1 proj1 = {}, Proj2 proj2 = {});
template<@\libconcept{input_range}@ R1, @\libconcept{input_range}@ R2, class Pred = ranges::equal_to,
class Proj1 = identity, class Proj2 = identity>
requires (@\libconcept{forward_range}@<R1> || @\libconcept{sized_range}@<R1>) &&
(@\libconcept{forward_range}@<R2> || @\libconcept{sized_range}@<R2>) &&
@\libconcept{indirectly_comparable}@<iterator_t<R1>, iterator_t<R2>, Pred, Proj1, Proj2>
constexpr bool ends_with(R1&& r1, R2&& r2, Pred pred = {},
Proj1 proj1 = {}, Proj2 proj2 = {});
}

// \ref{alg.modifying.operations}, mutating sequence operations
// \ref{alg.copy}, copy
template<class InputIterator, class OutputIterator>
Expand Down Expand Up @@ -4219,6 +4249,81 @@
\tcode{Searcher} need not meet the \oldconcept{CopyConstructible} requirements.
\end{itemdescr}

\rSec2[alg.starts.with]{Starts with}

\indexlibraryglobal{starts_with}%
\begin{itemdecl}
template<@\libconcept{input_iterator}@ I1, @\libconcept{sentinel_for}@<I1> S1, @\libconcept{input_iterator}@ I2, @\libconcept{sentinel_for}@<I2> S2,
class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity>
requires @\libconcept{indirectly_comparable}@<I1, I2, Pred, Proj1, Proj2>
constexpr bool ranges::starts_with(I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = {},
Proj1 proj1 = {}, Proj2 proj2 = {});
template<@\libconcept{input_range}@ R1, @\libconcept{input_range}@ R2, class Pred = ranges::equal_to, class Proj1 = identity,
class Proj2 = identity>
requires @\libconcept{indirectly_comparable}@<iterator_t<R1>, iterator_t<R2>, Pred, Proj1, Proj2>
constexpr bool ranges::starts_with(R1&& r1, R2&& r2, Pred pred = {},
Proj1 proj1 = {}, Proj2 proj2 = {});
Comment on lines +4261 to +4265
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@jwakely: I'm not sure why this second overload doesn't have a specification, but that's what's in the paper. Please let me know if anything is missing here (or if this is covered by some blanket wording elsewhere).

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The range overloads map to the first/last overloads per [algorithms.requirements] p14.

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Aha, thanks!

\end{itemdecl}

\begin{itemdescr}
\pnum
\returns
\begin{codeblock}
ranges::mismatch(std::move(first1), last1, std::move(first2), last2,
pred, proj1, proj2).in2 == last2
\end{codeblock}
\end{itemdescr}

\rSec2[alg.ends.with]{Ends with}

\indexlibraryglobal{ends_with}%
\begin{itemdecl}
template<@\libconcept{input_iterator}@ I1, @\libconcept{sentinel_for}@<I1> S1, @\libconcept{input_iterator}@ I2, @\libconcept{sentinel_for}@<I2> S2,
class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity>
requires (@\libconcept{forward_iterator}@<I1> || @\libconcept{sized_sentinel_for}@<S1, I1>) &&
(@\libconcept{forward_iterator}@<I2> || @\libconcept{sized_sentinel_for}@<S2, I2>) &&
@\libconcept{indirectly_comparable}@<I1, I2, Pred, Proj1, Proj2>
constexpr bool ranges::ends_with(I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = {},
Proj1 proj1 = {}, Proj2 proj2 = {});
\end{itemdecl}

\begin{itemdescr}
\pnum
Let \tcode{N1} be \tcode{last1 - first1} and
\tcode{N2} be \tcode{last2 - first2}.

\pnum
\returns
\tcode{false} if $\tcode{N1} < \tcode{N2}$, otherwise
\begin{codeblock}
ranges::equal(std::move(first1) + (N1 - N2), last1, std::move(first2), last2,
pred, proj1, proj2)
\end{codeblock}
\end{itemdescr}

\begin{itemdecl}
template<@\libconcept{input_range}@ R1, @\libconcept{input_range}@ R2, class Pred = ranges::equal_to, class Proj1 = identity,
class Proj2 = identity>
requires (@\libconcept{forward_range}@<R1> || @\libconcept{sized_range}@<R1>) &&
(@\libconcept{forward_range}@<R2> || @\libconcept{sized_range}@<R2>) &&
@\libconcept{indirectly_comparable}@<iterator_t<R1>, iterator_t<R2>, Pred, Proj1, Proj2>
constexpr bool ranges::ends_with(R1&& r1, R2&& r2, Pred pred = {},
Proj1 proj1 = {}, Proj2 proj2 = {});
\end{itemdecl}

\begin{itemdescr}
\pnum
Let \tcode{N1} be \tcode{ranges::distance(r1)} and
\tcode{N2} be \tcode{ranges::distance(r2)}.

\pnum
\returns
\tcode{false} if $\tcode{N1} < \tcode{N2}$, otherwise
\begin{codeblock}
ranges::equal(ranges::drop_view(ranges::ref_view(r1), N1 - N2), r2, pred, proj1, proj2)
\end{codeblock}
\end{itemdescr}

\rSec1[alg.modifying.operations]{Mutating sequence operations}

\rSec2[alg.copy]{Copy}
Expand Down
1 change: 1 addition & 0 deletions source/support.tex
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Expand Up @@ -661,6 +661,7 @@
#define @\defnlibxname{cpp_lib_quoted_string_io}@ 201304L // also in \libheader{iomanip}
#define @\defnlibxname{cpp_lib_ranges}@ 201911L
// also in \libheader{algorithm}, \libheader{functional}, \libheader{iterator}, \libheader{memory}, \libheader{ranges}
#define @\defnlibxname{cpp_lib_ranges_starts_ends_with}@ 202106L // also in \libheader{algorithm}
#define @\defnlibxname{cpp_lib_raw_memory_algorithms}@ 201606L // also in \libheader{memory}
#define @\defnlibxname{cpp_lib_remove_cvref}@ 201711L // also in \libheader{type_traits}
#define @\defnlibxname{cpp_lib_result_of_sfinae}@ 201210L // also in \libheader{functional}, \libheader{type_traits}
Expand Down