channel api cleanup

examples/concurrency.cc

@@ -12,10 +12,9 @@ int main() {
             c.put(foldl(half, 0));
         };
         spawn(sched, f, c, arr.slice(0, arr.size() / 2));
-        spawn(sched, f, c, arr.slice(arr.size() / 2, arr.size()));
+        spawn(sched, f, c, arr + (arr.size() / 2));
 
-        int a, b;
-        c.get(a), c.get(b);
+        int a = c.get(), b = c.get();
         writefln("%s + %s = %s", a, b, a + b);
     };
 

ostd/channel.hh

@@ -46,8 +46,11 @@ struct channel {
         p_state->put(std::move(val));
     }
 
-    bool get(T &val) {
-        return p_state->get(val, true);
+    T get() {
+        T ret;
+        /* guaranteed to return true if at all */
+        p_state->get(ret, true);
+        return ret;
     }
 
     bool try_get(T &val) {
@@ -87,9 +90,12 @@ private:
                 }
             }
             if (p_messages.empty()) {
+                if (p_closed) {
+                    throw channel_error{"get from a closed channel"};
+                }
                 return false;
             }
-            val = p_messages.front();
+            val = std::move(p_messages.front());
             p_messages.pop_front();
             return true;
         }