signal: simplify the implementation of the cookie and signal
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228
signal.hpp
228
signal.hpp
@ -12,114 +12,126 @@
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#include "debug/assert.hpp"
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#include <functional>
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#include <list>
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namespace cruft {
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namespace reduce {
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/// Returns the short-circuited logical-and of the results of all
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/// connected callbacks.
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struct logical_and {
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template <typename InputT, typename ...Args>
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decltype(auto)
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operator() (InputT first, InputT last, Args&&... args)
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{
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while (first != last)
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if (!(std::invoke (*first++, args...)))
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return false;
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return true;
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}
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};
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/// Returns the short-circuited logical-or of the results of all
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/// connected callbacks.
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struct logical_or {
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template <typename InputT, typename ...Args>
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decltype(auto)
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operator() (InputT first, InputT last, Args&&... args)
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{
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while (first != last)
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if (std::invoke (*first++, args...))
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return true;
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return false;
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}
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};
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/// Unconditionally evaluates all connected callbacks. Returns nothing.
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struct noop {
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template <typename InputT, typename ...Args>
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void operator() (InputT first, InputT last, Args&&... args)
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{
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while (first != last) {
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std::invoke (*first++, args...);
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}
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}
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};
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}
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/// A signal object whose clients can listen for invocations.
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///
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/// The arguments supplied to the invocation of the parent are supplied
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/// to the callback of each child.
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///
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/// Every client must store the cookie from `connect`. When this goes out
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/// of scope it will disconnect the callback from the signal object.
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/// It is permissible to release a cookie while it is being invoked, but
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/// no other cookie for the duration.
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///
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/// All cookies _should_ be destroyed or released before the signal is
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/// destroyed.
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///
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/// \tparam FunctionT The type of the callback
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template <
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typename FunctionT,
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typename ReductionT = reduce::noop
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typename FunctionT
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>
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class signal {
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public:
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using reduction_type = ReductionT;
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using function_type = FunctionT;
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typedef std::list<FunctionT> group;
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///////////////////////////////////////////////////////////////////////
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/// A single node in a doubly linked list of callbacks to invoke when
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/// a signal is invoked.
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///
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/// They perform no direct processing by themselves. Instead they are
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/// entirely focused on managing lifetimes of, and pointers to, the
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/// callbacks that will be invoked.
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struct cookie {
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cookie (cookie const&) = delete;
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cookie& operator= (cookie const&) = delete;
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cookie (typename group::iterator _position,
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signal<FunctionT,ReductionT> &_parent):
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m_position (_position),
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m_parent (_parent)
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cookie (FunctionT &&_callback)
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: callback (std::move (_callback))
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, next (nullptr)
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, prev (nullptr)
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{ ; }
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cookie (cookie &&rhs) noexcept:
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m_position (rhs.m_position),
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m_parent (rhs.m_parent)
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cookie (cookie &&rhs) noexcept
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: cookie (std::move (rhs.callback))
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{
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rhs.m_position = rhs.m_parent.m_children.end ();
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replace (rhs);
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}
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cookie& operator= (cookie &&rhs) noexcept
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{
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CHECK_EQ (&m_parent, &rhs.m_parent);
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std::swap (m_position, rhs.m_position);
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replace (rhs);
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callback = std::move (rhs.callback);
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return *this;
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}
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cookie (cookie const&) = delete;
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cookie& operator= (cookie const&) = delete;
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~cookie ()
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{
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if (m_parent.m_children.end () != m_position)
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m_parent.disconnect (*this);
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release ();
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}
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void reset (FunctionT &&cb)
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/// Take the position of `rhs` in the linked list.
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void replace (cookie &rhs)
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{
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*m_position = std::move (cb);
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// It could be more efficient to special case these
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// operations but this shouldn't be an operation that
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// occurs in a hot loop anyway.
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release ();
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rhs.append (*this);
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rhs.release ();
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}
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/// Link the provided cookie into the linked list as our
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/// successor.
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///
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/// The provided cookie must not currently be part of any
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/// linked list.
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void append (cookie &rhs)
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{
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CHECK (rhs.next == nullptr);
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CHECK (rhs.prev == nullptr);
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typename group::iterator m_position;
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signal<FunctionT,ReductionT> &m_parent;
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if (next) {
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CHECK_EQ (next->prev, this);
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next->prev = &rhs;
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}
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rhs.next = next;
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rhs.prev = this;
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next = &rhs;
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}
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/// If this cookie is part of a linked list then remove it
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/// from the linked list. Otherwise this is a noop.
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void release (void)
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{
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if (next) next->prev = prev;
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if (prev) prev->next = next;
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next = nullptr;
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prev = nullptr;
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}
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FunctionT callback;
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/// The next node in the linked list. Or nullptr if this is the end.
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cookie *next;
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/// The previous node in the linked list. Or nullptr if this is the start.
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cookie *prev;
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};
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public:
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signal () = default;
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signal ()
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: m_head (FunctionT{})
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{ ; }
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signal (signal const&) = default;
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signal& operator= (signal const&) = default;
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signal (signal &&) noexcept = default;
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signal& operator= (signal &&) noexcept = default;
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signal (signal const&) = delete;
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signal& operator= (signal const&) = delete;
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signal (signal &&rhs) noexcept = default;
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signal& operator= (signal &&rhs) noexcept = default;
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~signal ()
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{
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@ -127,65 +139,59 @@ namespace cruft {
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}
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/// Add a callback to list.
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cookie connect [[nodiscard]] (FunctionT &&_cb)
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cookie
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connect [[nodiscard]] (FunctionT &&_callback)
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{
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return cookie (
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m_children.insert (
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m_children.end (),
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std::move (_cb)
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),
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*this
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);
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cookie res (std::move (_callback));
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m_head.append (res);
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return res;
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}
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cookie connect [[nodiscard]] (FunctionT const &_cb)
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{
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return cookie (
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m_children.insert (
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m_children.end (),
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std::move (_cb)
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),
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*this
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);
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}
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void disconnect (cookie &c)
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{
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m_children.erase (c.m_position);
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c.m_position = m_children.end ();
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}
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/// Disconnect all callbacks
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void clear (void)
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{
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m_children.clear ();
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}
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void clear (void);
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/// Returns the number of callbacks connected.
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size_t size (void) const
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std::size_t size (void) const
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{
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return m_children.size ();
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std::size_t accum = 0;
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for (auto cursor = m_head.next; cursor; cursor = cursor->next)
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++accum;
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return accum;
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}
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bool empty (void) const
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{
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return m_children.empty ();
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return m_head.next == nullptr;
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}
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/// Execute all callbacks
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template <typename ...ArgsT>
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decltype(auto)
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operator() (ArgsT&&... tail)
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{
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return ReductionT {} (
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m_children.begin (),
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m_children.end (),
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std::forward<ArgsT> (tail)...
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);
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// We need to cache the cursor and advance _before_ we invoke
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// the cookie so that we have saved a pointer to the next
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// child in case it gets released on us during the call.
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cookie *cursor = m_head.next;
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while (cursor) {
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auto now = cursor;
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cursor = cursor->next;
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std::invoke (now->callback, tail...);
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}
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}
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private:
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group m_children;
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/// The first node in the linked list of callbacks. We
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/// unconditionally store this node to simplify anchoring the
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/// linked list to the signal object and removing nodes via their
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/// destructors.
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cookie m_head;
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};
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@ -72,57 +72,26 @@ test_value_signal (cruft::TAP::logger &tap)
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///////////////////////////////////////////////////////////////////////////////
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void
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test_combiner (cruft::TAP::logger &tap)
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{
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{
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cruft::signal<std::function<bool(void)>, cruft::reduce::logical_and> sig;
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unsigned count = 0;
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auto cookie0 = sig.connect ([&] (void) { ++count; return true; });
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auto cookie1 = sig.connect ([&] (void) { ++count; return true; });
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auto cookie2 = sig.connect ([&] (void) { ++count; return true; });
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tap.expect (sig (), "bool signal, success");
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tap.expect_eq (count, 3u, "bool signal, success, count");
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}
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{
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cruft::signal<std::function<bool(void)>, cruft::reduce::logical_and> sig;
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unsigned count = 0;
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auto cookie0 = sig.connect ([&] (void) { ++count; return true; });
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auto cookie1 = sig.connect ([&] (void) { ++count; return false; });
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auto cookie2 = sig.connect ([&] (void) { ++count; return true; });
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tap.expect (!sig (), "bool signal, failure");
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// ordering of signals is not guaranteed so we can't say for sure how
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// many callbacks will be triggered; it will _probably_ be in order
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// though.
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tap.expect_le (count, 3u, "bool signal, failure, count");
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}
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}
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///////////////////////////////////////////////////////////////////////////////
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void
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test_disconnect (cruft::TAP::logger &tap)
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test_parallel_release (cruft::TAP::logger &tap)
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{
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tap.expect_nothrow ([] {
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using function_t = std::function<void(void)>;
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cruft::signal<function_t> sig;
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cruft::signal<function_t>::cookie a = sig.connect ([&] (void) { sig.disconnect (a); });
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cruft::signal<function_t>::cookie b = sig.connect ([&] (void) { sig.disconnect (b); });
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cruft::signal<function_t>::cookie c = sig.connect ([&] (void) { sig.disconnect (c); });
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cruft::signal<function_t>::cookie d = sig.connect ([&] (void) { sig.disconnect (d); });
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cruft::signal<function_t>::cookie a = sig.connect ([&] (void) { a.release (); });
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cruft::signal<function_t>::cookie b = sig.connect ([&] (void) { b.release (); });
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cruft::signal<function_t>::cookie c = sig.connect ([&] (void) { c.release (); });
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cruft::signal<function_t>::cookie d = sig.connect ([&] (void) { d.release (); });
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sig ();
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}, "parallel disconnect in invocation");
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}, "parallel release in invocation");
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}
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///////////////////////////////////////////////////////////////////////////////
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#include <iostream>
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int
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main (int, char **)
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{
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@ -131,7 +100,6 @@ main (int, char **)
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test_single (tap);
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test_double (tap);
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test_value_signal (tap);
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test_combiner (tap);
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test_disconnect (tap);
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test_parallel_release (tap);
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});
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}
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