P2387R3 Pipe support for user-defined range adaptors

Author: jensmaurer

source/ranges.tex

@@ -183,6 +183,11 @@
 
   namespace views { template<class T> inline constexpr @\unspec@ istream = @\unspec@; }
 
+  // \ref{range.adaptor.object}, range adaptor objects
+  template<class D>
+    requires is_class_v<D> && @\libconcept{same_as}@<D, remove_cv_t<D>>
+  class range_adaptor_closure { };
+
   // \ref{range.all}, all view
   namespace views {
     inline constexpr @\unspec@ all = @\unspec@;
@@ -3137,10 +3142,10 @@
 
 \pnum
 A \term{range adaptor closure object} is a unary function object that accepts
-a \libconcept{viewable_range} argument and returns a \libconcept{view}. For
+a \libconcept{range} argument. For
 a range adaptor closure object \tcode{C} and an expression \tcode{R} such that
-\tcode{decltype((R))} models \libconcept{viewable_range}, the following
-expressions are equivalent and yield a \libconcept{view}:
+\tcode{decltype((R))} models \libconcept{range}, the following
+expressions are equivalent:
 \begin{codeblock}
 C(R)
 R | C
@@ -3166,6 +3171,42 @@
 The expression \tcode{C | D} is well-formed if and only if
 the initializations of the state entities of \tcode{E} are all well-formed.
 
+\pnum
+Given an object \tcode{t} of type \tcode{T}, where
+\begin{itemize}
+\item
+\tcode{t} is a unary function object that accepts a \tcode{range} argument,
+\item
+\tcode{T} models \tcode{\libconcept{derived_from}<range_adaptor_closure<T>>},
+\item
+\tcode{T} has no other base classes of type \tcode{range_adaptor_closure<U>} for any other type \tcode{U}, and
+\item
+\tcode{T} does not model \tcode{range}
+\end{itemize}
+then the implementation ensures
+that \tcode{t} is a range adaptor closure object.
+
+\pnum
+The template parameter \tcode{D} for \tcode{range_adaptor_closure}
+may be an incomplete type.
+If an expression of type \cv{} \tcode{D}
+is used as an operand to the \tcode{|} operator,
+\tcode{D} shall be complete and
+model \tcode{\libconcept{derived_from}<range_adaptor_closure<D>>}.
+The behavior of an expression involving an object of type \cv{} \tcode{D}
+as an operand to the \tcode{|} operator is undefined
+if overload resolution selects a program-defined \tcode{operator|} function.
+
+\pnum
+If an expression of type \cv{} \tcode{U}
+is used as an operand to the \tcode{|} operator,
+where \tcode{U} has a base class of type \tcode{range_adaptor_closure<T>}
+for some type \tcode{T} other than \tcode{U}, the behavior is undefined.
+
+\pnum
+The behavior of a program
+that adds a specialization for \tcode{range_adaptor_closure} is undefined.
+
 \pnum
 A \term{range adaptor object} is a
 customization point object\iref{customization.point.object}

source/support.tex

@@ -573,6 +573,7 @@
 #define @\defnlibxname{cpp_lib_atomic_value_initialization}@       201911L // also in \libheader{atomic}, \libheader{memory}
 #define @\defnlibxname{cpp_lib_atomic_wait}@                       201907L // also in \libheader{atomic}
 #define @\defnlibxname{cpp_lib_barrier}@                           201907L // also in \libheader{barrier}
+#define @\defnlibxname{cpp_lib_bind_back}@                         202202L // also in \libheader{functional}
 #define @\defnlibxname{cpp_lib_bind_front}@                        201907L // also in \libheader{functional}
 #define @\defnlibxname{cpp_lib_bit_cast}@                          201806L // also in \libheader{bit}
 #define @\defnlibxname{cpp_lib_bitops}@                            201907L // also in \libheader{bit}
@@ -664,7 +665,7 @@
 #define @\defnlibxname{cpp_lib_parallel_algorithm}@                201603L // also in \libheader{algorithm}, \libheader{numeric}
 #define @\defnlibxname{cpp_lib_polymorphic_allocator}@             201902L // also in \libheader{memory_resource}
 #define @\defnlibxname{cpp_lib_quoted_string_io}@                  201304L // also in \libheader{iomanip}
-#define @\defnlibxname{cpp_lib_ranges}@                            202110L
+#define @\defnlibxname{cpp_lib_ranges}@                            202202L
   // 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_ranges_zip}@                        202110L // also in \libheader{ranges}, \libheader{tuple}, \libheader{utility}

source/utilities.tex

@@ -14090,9 +14090,9 @@
   // \ref{func.not.fn}, function template \tcode{not_fn}
   template<class F> constexpr @\unspec@ not_fn(F&& f);
 
-  // \ref{func.bind.front}, function template \tcode{bind_front}
+  // \ref{func.bind.partial}, function templates \tcode{bind_front} and \tcode{bind_back}
   template<class F, class... Args> constexpr @\unspec@ bind_front(F&&, Args&&...);
-
+  template<class F, class... Args> constexpr @\unspec@ bind_back(F&&, Args&&...);
   // \ref{func.bind}, bind
   template<class T> struct is_bind_expression;
   template<class T>
@@ -15736,19 +15736,23 @@
 Any exception thrown by the initialization of \tcode{fd}.
 \end{itemdescr}
 
-\rSec2[func.bind.front]{Function template \tcode{bind_front}}
+\rSec2[func.bind.partial]{Function templates \tcode{bind_front} and \tcode{bind_back}}
 
 \indexlibraryglobal{bind_front}%
+\indexlibraryglobal{bind_back}%
 \begin{itemdecl}
 template<class F, class... Args>
   constexpr @\unspec@ bind_front(F&& f, Args&&... args);
+template<class F, class... Args>
+  constexpr @\unspec@ bind_back(F&& f, Args&&... args);
 \end{itemdecl}
 
 \begin{itemdescr}
 \pnum
 Within this subclause:
 \begin{itemize}
-\item \tcode{g} is a value of the result of a \tcode{bind_front} invocation,
+\item \tcode{g} is a value of
+the result of a \tcode{bind_front} or \tcode{bind_back} invocation,
 \item \tcode{FD} is the type \tcode{decay_t<F>},
 \item \tcode{fd} is the target object of \tcode{g}\iref{func.def}
   of type \tcode{FD},
@@ -15784,7 +15788,15 @@
 \pnum
 \returns
 A perfect forwarding call wrapper \tcode{g}
-with call pattern \tcode{invoke(fd, bound_args..., call_args...)}.
+with call pattern:
+\begin{itemize}
+\item
+\tcode{invoke(fd, bound_args..., call_args...)}
+for a \tcode{bind_front} invocation, or
+\item
+\tcode{invoke(fd, call_args..., bound_args...)}
+for a \tcode{bind_back} invocation.
+\end{itemize}
 
 \pnum
 \throws

source/xrefdelta.tex

@@ -89,5 +89,8 @@
 \movedxref{ofstream.assign}{ofstream.swap}
 \movedxref{fstream.assign}{fstream.swap}
 
+% P2387R3 Pipe support for user-defined range adaptors
+\movedxref{func.bind.front}{func.bind.partial}
+
 % Deprecated features.
 %\deprxref{old.label}  (if moved to depr.old.label, otherwise use \movedxref)