use std::forward when parameter is universal reference

As discussed in #264

include/marl/dag.h

@@ -94,6 +94,7 @@ class DAGBase {
   struct Node {
     MARL_NO_EXPORT inline Node() = default;
     MARL_NO_EXPORT inline Node(Work&& work);
+    MARL_NO_EXPORT inline Node(const Work& work);
 
     // The work to perform for this node in the graph.
     Work work;
@@ -137,6 +138,9 @@ class DAGBase {
 template <typename T>
 DAGBase<T>::Node::Node(Work&& work) : work(std::move(work)) {}
 
+template <typename T>
+DAGBase<T>::Node::Node(const Work& work) : work(work) {}
+
 template <typename T>
 void DAGBase<T>::initCounters(RunContext* ctx, Allocator* allocator) {
   auto numCounters = initialCounters.size();
@@ -233,7 +237,7 @@ DAGNodeBuilder<T>::DAGNodeBuilder(DAGBuilder<T>* builder, NodeIndex index)
 template <typename T>
 template <typename F>
 DAGNodeBuilder<T> DAGNodeBuilder<T>::then(F&& work) {
-  auto node = builder->node(std::move(work));
+  auto node = builder->node(std::forward<F>(work));
   builder->addDependency(*this, node);
   return node;
 }
@@ -323,7 +327,7 @@ DAGNodeBuilder<T> DAGBuilder<T>::node(
               "NodeBuilder vectors out of sync");
   auto index = dag->nodes.size();
   numIns.emplace_back(0);
-  dag->nodes.emplace_back(Node{std::move(work)});
+  dag->nodes.emplace_back(Node{std::forward<F>(work)});
   auto node = DAGNodeBuilder<T>{this, index};
   for (auto in : after) {
     addDependency(in, node);

src/dag_test.cpp

@@ -173,3 +173,18 @@ TEST_P(WithBoundScheduler, DAGFanOutFanIn) {
               UnorderedElementsAre("E0", "E1", "E2", "E3"));
   ASSERT_THAT(data.order[11], "F");
 }
+
+TEST_P(WithBoundScheduler, DAGForwardFunc) {
+  marl::DAG<void>::Builder builder;
+  std::function<void()> func([](){});
+
+  ASSERT_TRUE(func);
+
+  auto a = builder.root()
+      .then(func)
+      .then(func);
+
+  builder.node(func, {a});
+
+  ASSERT_TRUE(func);
+}