From 6d6292cc9d2da6b570a3a44ede78b098fccd7537 Mon Sep 17 00:00:00 2001
From: Tom Smeding <tom.smeding@gmail.com>
Date: Sun, 1 Jul 2018 23:50:52 +0200
Subject: Actually break loop in Board::forEachMove

---
 ai_mm.cpp   |  1 +
 ai_rand.cpp |  3 ++-
 board.h     | 55 ++++++++++++++++++++++++++++---------------------------
 3 files changed, 31 insertions(+), 28 deletions(-)

diff --git a/ai_mm.cpp b/ai_mm.cpp
index 4400a84..10d2fae 100644
--- a/ai_mm.cpp
+++ b/ai_mm.cpp
@@ -94,6 +94,7 @@ Move AI::MM::findMove(const Board &bd, int player) {
 			bestScore = score;
 			bestMove = mv;
 		}
+		return false;
 	});
 
 	cerr << ']' << endl;
diff --git a/ai_rand.cpp b/ai_rand.cpp
index 9bd3eed..8b71670 100644
--- a/ai_rand.cpp
+++ b/ai_rand.cpp
@@ -5,8 +5,9 @@ Move AI::Rand::findMove(const Board &bd, int player) {
 	Move poss[N * N * N];
 	int nposs = 0;
 
-	bd.forEachMove(player, [&bd, &poss, &nposs](Move mv) {
+	bd.forEachMove(player, [&poss, &nposs](Move mv) {
 		poss[nposs++] = mv;
+		return false;
 	});
 
 	if (nposs == 0) return Move(-1, -1);
diff --git a/board.h b/board.h
index 1ab0646..3b0895d 100644
--- a/board.h
+++ b/board.h
@@ -3,6 +3,7 @@
 #include <iostream>
 #include <optional>
 #include <string_view>
+#include <type_traits>
 #include <cstdint>
 
 using namespace std;
@@ -37,8 +38,33 @@ struct Board {
 	// F should have a signature compatible with bool F(Move mv).
 	// If the callback returns true, iteration is stopped.
 	// Callback should not modify this Board instance.
-	template <typename F>
-	void forEachMove(int player, F callback) const;
+	template <typename F,
+	          typename = enable_if_t<is_invocable_r<bool, F, Move>::value>>
+	void forEachMove(int player, F callback) const {
+		static const int deltas[4][2] = {{-1, 0}, {0, -1}, {1, 0}, {0, 1}};
+
+		for (int y = 0; y < N; y++)
+		for (int x = 0; x < N; x++) {
+			uint8_t v = cells[N * y + x];
+			if (player == 1 ? v != WHITE && v != KING : v != BLACK) continue;
+
+			for (int i = 0; i < 4; i++) {
+				int x2 = x + deltas[i][0], y2 = y + deltas[i][1];
+				while (x2 >= 0 && x2 < N && y2 >= 0 && y2 < N) {
+					if (cells[N * y2 + x2] != EMPTY) break;
+					if (N * y2 + x2 != BOARDMID) {
+						bool ret = callback(Move(N * y + x, N * y2 + x2));
+						if (ret) goto stop_iteration;
+					}
+
+					x2 += deltas[i][0];
+					y2 += deltas[i][1];
+				}
+			}
+		}
+
+	stop_iteration: ;
+	}
 
 private:
 	Board();
@@ -51,28 +77,3 @@ private:
 
 ostream& operator<<(ostream &os, const Move &mv);
 ostream& operator<<(ostream &os, const Board &bd);
-
-
-template <typename F>
-void Board::forEachMove(int player, F callback) const {
-	static const int deltas[4][2] = {{-1, 0}, {0, -1}, {1, 0}, {0, 1}};
-
-	for (int y = 0; y < N; y++)
-	for (int x = 0; x < N; x++) {
-		uint8_t v = cells[N * y + x];
-		if (player == 1 ? v != WHITE && v != KING : v != BLACK) continue;
-
-		for (int i = 0; i < 4; i++) {
-			int x2 = x + deltas[i][0], y2 = y + deltas[i][1];
-			while (x2 >= 0 && x2 < N && y2 >= 0 && y2 < N) {
-				if (cells[N * y2 + x2] != EMPTY) break;
-				if (N * y2 + x2 != BOARDMID) {
-					callback(Move(N * y + x, N * y2 + x2));
-				}
-
-				x2 += deltas[i][0];
-				y2 += deltas[i][1];
-			}
-		}
-	}
-}
-- 
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