Data commit

Task/Null-object/Crystal/null-object.crystal

@@ -0,0 +1,14 @@
+foo : Int32 | Nil = 5 # this variable's type can be Int32 or Nil
+bar : Int32? = nil    # equivalent type to above, but shorter syntax
+baz : Int32 = 5       # this variable can never be nil
+
+foo.not_nil!          # nothing happens, since 5 is not nil
+puts "Is foo nil? #{foo.nil?}"
+foo = nil
+puts "Now is foo nil? #{foo.nil?}"
+
+puts "Does bar equal nil? #{bar == nil}"
+
+puts "Is bar equivalent to nil? #{bar === nil}"
+
+bar.not_nil!          # bar is nil, so an exception is thrown