arguments support

spec/std/db/dummy_driver.cr

@@ -8,7 +8,15 @@ class DummyDriver < DB::Driver
       super(driver)
     end
 
-    def exec(*args)
+    protected def add_parameter(index : Int32, value)
+      raise "not implemented"
+    end
+
+    protected def add_parameter(name : String, value)
+      raise "not implemented"
+    end
+
+    protected def execute
       DummyResultSet.new self, @items.each
     end
   end

src/db/statement.cr

@@ -5,6 +5,30 @@ module DB
     def initialize(@driver)
     end
 
-    abstract def exec(*args) : ResultSet
+    def exec(*args) : ResultSet
+      exec args
+    end
+
+    def exec(args : Enumerable)
+      before_execute
+      args.each_with_index(1) do |arg, index|
+        if arg.is_a?(Hash)
+          arg.each do |key, value|
+            add_parameter key.to_s, value
+          end
+        else
+          add_parameter index, arg
+        end
+      end
+      execute
+    end
+
+    protected def before_execute
+    end
+
+    # 1-based positional arguments
+    protected abstract def add_parameter(index : Int32, value)
+    protected abstract def add_parameter(name : String, value)
+    protected abstract def execute : ResultSet
   end
 end