Introduce `BoxIndicator` and `BoxTraverser` helper classes

`BoxIndicator` implements an indicator function for the world area. Together with `BoxTraverser` it is used to simplifiy action validation and area traversion.

3 files changed, 97 insertions, 37 deletions

diff --git a/src/box_indicator.h b/src/box_indicator.h
new file mode 100644
index 0000000..db750e4
--- /dev/null
+++ b/src/box_indicator.h
@@ -0,0 +1,40 @@
+#ifndef LIFE_SRC_BOX_INDICATOR_
+#define LIFE_SRC_BOX_INDICATOR_
+
+namespace life {
+namespace util {
+
+class BoxIndicator {
+	public:
+	   	BoxIndicator(
+			const std::size_t offset_x,
+			const std::size_t offset_y,
+			const std::size_t size_x,
+			const std::size_t size_y):
+			a_x_{offset_x},
+			a_y_{offset_y},
+			b_x_{a_x_ + size_x},
+			b_y_{a_y_ + size_y} { }
+
+	   	BoxIndicator(const std::size_t size_x, const std::size_t size_y):
+			BoxIndicator(0, 0, size_x, size_y) { }
+
+		bool operator()(const std::size_t x, const std::size_t y) const {
+			return x >= this->a_x_
+			    && x <  this->b_x_
+			    && y >= this->a_y_
+			    && y <  this->b_y_;
+		}
+	
+	protected:
+		const std::size_t a_x_;
+		const std::size_t a_y_;
+		const std::size_t b_x_;
+		const std::size_t b_y_;
+
+};
+		
+}
+}
+
+#endif  // LIFE_SRC_BOX_INDICATOR_
diff --git a/src/box_traverser.h b/src/box_traverser.h
new file mode 100644
index 0000000..1bc0edd
--- /dev/null
+++ b/src/box_traverser.h
@@ -0,0 +1,26 @@
+#ifndef LIFE_SRC_BOX_TRAVERSER_
+#define LIFE_SRC_BOX_TRAVERSER_
+
+#include <functional>
+
+#include "box_indicator.h"
+
+namespace life {
+namespace util {
+
+struct BoxTraverser : public BoxIndicator {
+	using BoxIndicator::BoxIndicator;
+
+	void for_each(const std::function<void(std::size_t, std::size_t)> f) const {
+		for ( std::size_t x = this->a_x_; x < this->b_x_; x++ ) {
+			for ( std::size_t y = this->a_y_; y < this->b_y_; y++ ) {
+				f(x, y);
+			}
+		}
+	}
+};
+
+}
+}
+
+#endif  // LIFE_SRC_BOX_TRAVERSER_
diff --git a/src/world.h b/src/world.h
index 72cc32f..b60c658 100644
--- a/src/world.h
+++ b/src/world.h
@@ -6,6 +6,8 @@
 #include <tuple>
 #include <cstdint>
 
+#include "box_traverser.h"
+
 namespace life {
 
 template<
@@ -14,19 +16,18 @@ template<
 >
 class World {
 	public:
-		World() {
-			for ( std::size_t j = 0; j < HEIGHT; j++ ) {
-				for ( std::size_t i = 0; i < WIDTH; i++ ) {
-					this->matrix_[j][i] = false;
-				}
-			}
+		static const std::size_t width  = WIDTH;
+		static const std::size_t height = HEIGHT;
+
+		World():
+			area_(width, height) {
+			this->area_.for_each([&](std::size_t i, std::size_t j) {
+				this->matrix_[j][i] = false;
+			});
 		}
 
 		bool isLifeAt(std::ptrdiff_t x, std::ptrdiff_t y) const {
-			if ( x >= 0      &&
-			     x <  WIDTH  &&
-			     y >= 0      &&
-			     y <  HEIGHT ) {
+			if ( this->area_(x, y) ) {
 				return this->matrix_[y][x];
 			} else {
 				return false; // end of world is dead
@@ -69,19 +70,13 @@ class World {
 		}
 
 		void summonLifeAt(std::size_t x, std::size_t y) {
-			if ( x >= 0      &&
-			     x <  WIDTH  &&
-			     y >= 0      &&
-			     y <  HEIGHT ) {
+			if ( this->area_(x, y) ) {
 				this->matrix_[y][x] = true;
 			}
 		}
 
 		void extinguishLifeAt(std::size_t x, std::size_t y) {
-			if ( x >= 0      &&
-			     x <  WIDTH  &&
-			     y >= 0      &&
-			     y <  HEIGHT ) {
+			if ( this->area_(x, y) ) {
 				this->matrix_[y][x] = false;
 			}
 		}
@@ -91,25 +86,23 @@ class World {
 
 			std::stack<std::tuple<std::size_t, std::size_t, bool>> updates;
 
-			for ( std::size_t j = 0; j < HEIGHT; j++ ) {
-				for ( std::size_t i = 0; i < WIDTH; i++ ) {
-					const std::uint8_t d = this->lifeDensityAt(i, j);
-
-					if ( this->matrix_[j][i] ) {
-						if ( d < 2 ) {
-							updates.push(std::make_tuple(i, j, false));	
-						} else if ( d == 2 || d == 3 ) {
-							updates.push(std::make_tuple(i, j, true));	
-						} else if ( d > 3 ) {
-							updates.push(std::make_tuple(i, j, false));	
-						}
-					} else {
-						if ( d == 3 ) {
-							updates.push(std::make_tuple(i, j, true));	
-						}
+			this->area_.for_each([&](std::size_t i, std::size_t j) {
+				const std::uint8_t d = this->lifeDensityAt(i, j);
+
+				if ( this->matrix_[j][i] ) {
+					if ( d < 2 ) {
+						updates.push(std::make_tuple(i, j, false));
+					} else if ( d == 2 || d == 3 ) {
+						updates.push(std::make_tuple(i, j, true));
+					} else if ( d > 3 ) {
+						updates.push(std::make_tuple(i, j, false));
+					}
+				} else {
+					if ( d == 3 ) {
+						updates.push(std::make_tuple(i, j, true));
 					}
 				}
-			}
+			});
 
 			while ( !updates.empty() ) {
 				const auto& update = updates.top();
@@ -125,14 +118,15 @@ class World {
 						std::get<1>(update)
 					);
 				}
-				
+
 				updates.pop();
 			}
 		}
 
 	private:
-		std::size_t age_ = 0;
+		const util::BoxTraverser area_;
 
+		std::size_t age_ = 0;
 		std::array<std::array<bool, WIDTH>, HEIGHT> matrix_;
 
 };