wpiutil: Add a signal-slot implementation. (#1163)

Imported from https://github.com/palacaze/sigslot

Classes were renamed from lowercase_me to UppercaseMe style, primarily
to avoid conflicting with the C standard library "signal" function.  They
were also moved to the "wpi::sig" namespace.

wpiutil/src/test/native/cpp/sigslot/signal-tracking.cpp

@@ -0,0 +1,181 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2018 FIRST. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+/*
+
+Sigslot, a signal-slot library
+
+https://github.com/palacaze/sigslot
+
+MIT License
+
+Copyright (c) 2017 Pierre-Antoine Lacaze
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+ */
+
+#include "wpi/Signal.h"  // NOLINT(build/include_order)
+
+#include "gtest/gtest.h"  // NOLINT(build/include_order)
+
+#include <cmath>
+#include <sstream>
+#include <string>
+
+using namespace wpi::sig;
+
+namespace {
+
+int sum = 0;
+
+void f1(int i) { sum += i; }
+struct o1 {
+  void operator()(int i) { sum += 2 * i; }
+};
+
+struct s {
+  void f1(int i) { sum += i; }
+  void f2(int i) const { sum += 2 * i; }
+};
+
+struct oo {
+  void operator()(int i) { sum += i; }
+  void operator()(double i) { sum += std::round(4 * i); }
+};
+
+struct dummy {};
+
+static_assert(trait::is_callable_v<trait::typelist<int>, decltype(&s::f1),
+                                   std::shared_ptr<s>>,
+              "");
+
+}  // namespace
+
+namespace wpi {
+
+TEST(Signal, TrackShared) {
+  sum = 0;
+  Signal<int> sig;
+
+  auto s1 = std::make_shared<s>();
+  sig.connect(&s::f1, s1);
+
+  auto s2 = std::make_shared<s>();
+  std::weak_ptr<s> w2 = s2;
+  sig.connect(&s::f2, w2);
+
+  sig(1);
+  ASSERT_EQ(sum, 3);
+
+  s1.reset();
+  sig(1);
+  ASSERT_EQ(sum, 5);
+
+  s2.reset();
+  sig(1);
+  ASSERT_EQ(sum, 5);
+}
+
+TEST(Signal, TrackOther) {
+  sum = 0;
+  Signal<int> sig;
+
+  auto d1 = std::make_shared<dummy>();
+  sig.connect(f1, d1);
+
+  auto d2 = std::make_shared<dummy>();
+  std::weak_ptr<dummy> w2 = d2;
+  sig.connect(o1(), w2);
+
+  sig(1);
+  ASSERT_EQ(sum, 3);
+
+  d1.reset();
+  sig(1);
+  ASSERT_EQ(sum, 5);
+
+  d2.reset();
+  sig(1);
+  ASSERT_EQ(sum, 5);
+}
+
+TEST(Signal, TrackOverloadedFunctionObject) {
+  sum = 0;
+  Signal<int> sig;
+  Signal<double> sig1;
+
+  auto d1 = std::make_shared<dummy>();
+  sig.connect(oo{}, d1);
+  sig(1);
+  ASSERT_EQ(sum, 1);
+
+  d1.reset();
+  sig(1);
+  ASSERT_EQ(sum, 1);
+
+  auto d2 = std::make_shared<dummy>();
+  std::weak_ptr<dummy> w2 = d2;
+  sig1.connect(oo{}, w2);
+  sig1(1);
+  ASSERT_EQ(sum, 5);
+
+  d2.reset();
+  sig1(1);
+  ASSERT_EQ(sum, 5);
+}
+
+TEST(Signal, TrackGenericLambda) {
+  std::stringstream s;
+
+  auto f = [&](auto a, auto... args) {
+    using result_t = int[];
+    s << a;
+    result_t r{
+        1,
+        ((void)(s << args), 1)...,
+    };
+    (void)r;
+  };
+
+  Signal<int> sig1;
+  Signal<std::string> sig2;
+  Signal<double> sig3;
+
+  auto d1 = std::make_shared<dummy>();
+  sig1.connect(f, d1);
+  sig2.connect(f, d1);
+  sig3.connect(f, d1);
+
+  sig1(1);
+  sig2("foo");
+  sig3(4.1);
+  ASSERT_EQ(s.str(), "1foo4.1");
+
+  d1.reset();
+  sig1(2);
+  sig2("bar");
+  sig3(3.0);
+  ASSERT_EQ(s.str(), "1foo4.1");
+}
+
+}  // namespace wpi