Fix the second valueFn call in (*MapOf) LoadOrCompute (#66)

mapof.go

@@ -229,7 +229,7 @@ func (m *MapOf[K, V]) doStore(key K, valueFn func() V, loadIfExists bool) (V, bo
 					topHashes = atomic.LoadUint64(&emptyb.topHashMutex)
 					atomic.StoreUint64(&emptyb.topHashMutex, storeTopHash(hash, topHashes, emptyidx))
 					value := valueFn()
-					var wv interface{} = valueFn()
+					var wv interface{} = value
 					atomic.StorePointer(&emptyb.values[emptyidx], unsafe.Pointer(&wv))
 					atomic.StorePointer(&emptyb.keys[emptyidx], unsafe.Pointer(&key))
 					unlockBucket(&rootb.topHashMutex)

mapof_test.go

@@ -395,6 +395,20 @@ func TestMapOfSerialLoadOrCompute(t *testing.T) {
 			t.Errorf("values do not match for %d: %v", i, v)
 		}
 	}
+
+	t.Run("valueFn func should be called only once", func(t *testing.T) {
+		m := NewIntegerMapOf[int, int]()
+		for i := 0; i < 100; {
+			m.LoadOrCompute(i, func() (v int) { v, i = i, i+1; return v })
+		}
+
+		m.Range(func(k, v int) bool {
+			if k != v {
+				t.Fatalf("%dth key is not equal to value %d", k, v)
+			}
+			return true
+		})
+	})
 }
 
 func TestMapOfSerialStoreThenDelete(t *testing.T) {