Merge pull request #6 from silverweed/flyweight

Add Flyweight

README.md

@@ -27,6 +27,7 @@ The goal is to have a set of [GOF patterns](http://www.blackwasp.co.uk/gofpatter
   - [Composite](structural/composite.cr)
   - [Decorator](structural/decorator.cr)
   - [Facade](structural/facade.cr)
+  - [Flyweight](structural/flyweight.cr)
 
 ## Contribution
 

structural/flyweight.cr

@@ -0,0 +1,81 @@
+# The flyweight pattern is a design pattern that is used to minimise
+# resource usage when working with very large numbers of objects.
+# When creating many thousands of identical objects, stateless flyweights
+# can lower the memory used to a manageable level.
+
+alias Position = {Int32, Int32}
+
+# Contains the extrinsic actions that the object can do.
+abstract class FlyweightTree
+  abstract def draw_at(pos : Position)
+end
+
+# Implements the Flyweight interface, optionally keeping an extrinsic state
+# which can be manipulated via that interface.
+class Tree < FlyweightTree
+  property pos
+
+  def initialize(species : String)
+    # Intrinsic (stateless) properties. These are shared between all instances of this tree.
+    @species = species
+    # Estrinsic (stateful) properties. These are accessed via the abstract interface
+    # provided by FlyweightTree
+    @pos = {0, 0}
+  end
+
+  def draw_at(_pos : Position)
+    pos = _pos
+    puts "Drawing #{@species} at #{pos}"
+  end
+end
+
+# Factory class for the flyweight objects.
+class Forest
+  def initialize
+    @trees = {} of String => FlyweightTree
+  end
+
+  def get_tree(species : String)
+    if @trees.has_key?(species)
+      @trees[species]
+    else
+      Tree.new(species).tap { |tree| @trees[species] = tree }
+    end
+  end
+
+  def tot_instances
+    @trees.size
+  end
+end
+
+# Client code
+forest = Forest.new
+forest.get_tree("birch").draw_at({5, 6})
+forest.get_tree("acacia").draw_at({3, 1})
+forest.get_tree("magnolia").draw_at({15, 86})
+forest.get_tree("birch").draw_at({8, 15})
+forest.get_tree("acacia").draw_at({18, 4})
+forest.get_tree("baobab").draw_at({1, 41})
+forest.get_tree("magnolia").draw_at({80, 50})
+forest.get_tree("acacia").draw_at({22, 3})
+forest.get_tree("birch").draw_at({1, 42})
+forest.get_tree("baobab").draw_at({15, 7})
+forest.get_tree("acacia").draw_at({33, 49})
+forest.get_tree("magnolia").draw_at({0, 0})
+puts "-----------------------"
+puts "Total instances created: #{forest.tot_instances}"
+
+# Drawing birch at {5, 6}
+# Drawing acacia at {3, 1}
+# Drawing magnolia at {15, 86}
+# Drawing birch at {8, 15}
+# Drawing acacia at {18, 4}
+# Drawing baobab at {1, 41}
+# Drawing magnolia at {80, 50}
+# Drawing acacia at {22, 3}
+# Drawing birch at {1, 42}
+# Drawing baobab at {15, 7}
+# Drawing acacia at {33, 49}
+# Drawing magnolia at {0, 0}
+# -----------------------
+# Total instances created: 4