From 9418a95824a24057f6733155e8266d41e0b9758d Mon Sep 17 00:00:00 2001
From: Jens Maurer <Jens.Maurer@gmx.net>
Date: Wed, 9 Jun 2021 17:47:24 +0200
Subject: [PATCH] P1659R3 starts_with and ends_with

---
 source/algorithms.tex | 105 ++++++++++++++++++++++++++++++++++++++++++
 source/support.tex    |   1 +
 2 files changed, 106 insertions(+)

diff --git a/source/algorithms.tex b/source/algorithms.tex
index e1e1a470c4..d5b735317a 100644
--- a/source/algorithms.tex
+++ b/source/algorithms.tex
@@ -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>
@@ -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 = {});
+\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}
diff --git a/source/support.tex b/source/support.tex
index fbd2b51ab5..fa649bab01 100644
--- a/source/support.tex
+++ b/source/support.tex
@@ -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}