FutureMoves: initial move to not storing board

src/logic/future_moves.rs

@@ -19,6 +19,8 @@ pub struct FutureMoves {
     agent_color: Piece,
 
     config: FutureMoveConfig,
+
+    board: Board,
 }
 
 #[derive(Copy, Clone)]
@@ -87,6 +89,7 @@ impl FutureMoves {
             current_depth: 0,
             agent_color,
             config,
+            board: Board::new(),
         }
     }
 
@@ -196,13 +199,15 @@ impl FutureMoves {
         let parent = &self.arena[parent_idx];
 
         let new_color = !parent.color;
+        let parent_board = self
+            .get_board_from_idx(parent_idx)
+            .expect("unable to get board");
 
         // use [`Board::all_positions`] here instead of [`Board::possible_moves`]
         // because we use [`Board::what_if`] later and we want to reduce calls to [`Board::propegate_from_dry`]
         let mut new: Vec<Move> = Board::all_positions()
             .flat_map(|coord| {
-                parent
-                    .board
+                parent_board
                     .what_if(coord, new_color)
                     .map(move |x| (coord, x))
             })
@@ -212,7 +217,7 @@ impl FutureMoves {
             .collect();
 
         if new.is_empty() {
-            new.push(Move::new(None, parent.board, new_color, self.agent_color));
+            new.push(Move::new(None, parent_board, new_color, self.agent_color));
         }
 
         let start_idx = self.arena.len();
@@ -321,7 +326,7 @@ impl FutureMoves {
 
     fn get_board_from_idx(&self, idx: usize) -> Option<Board> {
         if let Some(hist) = self.move_history(idx) {
-            let mut board = self.arena[self.current_root.unwrap()].board;
+            let mut board = self.board;
             for (m, c) in hist {
                 if let Some(m) = m {
                     board.place(m, c).expect("move would not propegate");
@@ -361,7 +366,8 @@ impl FutureMoves {
             // match the agent_color usually root or great-grand child
             .filter(|&idx| self.depth_of(idx) % 2 == 0)
             .find(|&idx| {
-                &self.arena[idx].board == board && self.arena[idx].color == !self.agent_color
+                self.get_board_from_idx(idx).as_ref() == Some(board)
+                    && self.arena[idx].color == !self.agent_color
             });
 
         if let Some(curr_board_idx) = curr_board {
@@ -577,7 +583,6 @@ mod tests {
 
         futm.arena.push(Move {
             coord: None,
-            board: Board::new(),
             winner: Winner::None,
             parent: None,
             children: Vec::new(),
@@ -664,7 +669,6 @@ mod tests {
 
         futm.arena.push(Move {
             coord: None,
-            board: Board::new(),
             winner: Winner::None,
             parent: None,
             children: vec![],
@@ -705,7 +709,6 @@ mod tests {
 
         futm.arena.push(Move {
             coord: None,
-            board: Board::new(),
             winner: Winner::None,
             parent: None,
             children: vec![1],