counter: Use a constructor

counter/counter.go

@@ -7,6 +7,10 @@ type Counter struct {
 	mutex sync.Mutex
 }
 
+func NewCounter() *Counter {
+	return &Counter{}
+}
+
 func (c *Counter) Inc() {
 	c.mutex.Lock()
 	defer c.mutex.Unlock()

counter/counter_test.go

@@ -16,18 +16,18 @@ func assertCounter(t testing.TB, got *Counter, want int) {
 
 func TestCounter(t *testing.T) {
 	t.Run("incrementing the counter 3 times leaves it at 3", func(t *testing.T) {
-		counter := Counter{}
+		counter := NewCounter()
 
 		counter.Inc()
 		counter.Inc()
 		counter.Inc()
 
-		assertCounter(t, &counter, 3)
+		assertCounter(t, counter, 3)
 	})
 
 	t.Run("it runs safely concurrently", func(t *testing.T) {
 		wantedCount := 1000
-		counter := Counter{}
+		counter := NewCounter()
 
 		var wg sync.WaitGroup
 		wg.Add(wantedCount)
@@ -39,6 +39,6 @@ func TestCounter(t *testing.T) {
 			}()
 		}
 		wg.Wait()
-		assertCounter(t, &counter, wantedCount)
+		assertCounter(t, counter, wantedCount)
 	})
 }