diff --git a/src/lib.rs b/src/lib.rs
index b921576..efbaec1 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -189,6 +189,8 @@ struct State {
 }
 
 impl State {
+    const DIR_POS: &'static [Pos] = &[Pos(0, -1), Pos(0, 1), Pos(-1, 0), Pos(1, 0)];
+
     fn new(lvl: Level) -> Self {
         State { lvl }
     }
@@ -250,10 +252,9 @@ impl State {
     }
 
     fn test_box(&self, pos: Pos, bt: bool) -> bool {
-        let dir: &[Pos] = &[Pos(0, -1), Pos(0, 1), Pos(-1, 0), Pos(1, 0)];
         let mut mbc = 0;
 
-        for i in dir {
+        for i in Self::DIR_POS {
             match self.lvl[pos + *i] {
                 Cell::Goal(false) | Cell::None => {
                     let dpos = pos - *i;