introduce database as driver wrapper.

expose list of types to support by the drivers implementors.
deal with nilable types with `#read?(T.class) : T?` methods.
change `#has_next` to `#move_next`

src/db/database.cr

@@ -0,0 +1,20 @@
+module DB
+  # Acts as an entry point for database access.
+  # Offers a com
+  class Database
+    getter driver_class
+    getter options
+
+    def initialize(@driver_class, @options)
+      @driver = @driver_class.new(@options)
+    end
+
+    def prepare(query)
+      @driver.prepare(query)
+    end
+
+    def exec(query, *args)
+      prepare(query).exec(*args)
+    end
+  end
+end

src/db/db.cr

@@ -1,4 +1,6 @@
 module DB
+  TYPES = [String, Int32, Int64, Float32, Float64]
+
   def self.driver_class(name) # : Driver.class
     @@drivers.not_nil![name]
   end
@@ -8,11 +10,12 @@ module DB
     @@drivers.not_nil![name] = klass
   end
 
-  def self.driver(name, options)
-    driver_class(name).new(options)
+  def self.open(name, options)
+    Database.new(driver_class(name), options)
   end
 end
 
+require "./database"
 require "./driver"
 require "./statement"
 require "./result_set"

src/db/result_set.cr

@@ -6,32 +6,21 @@ module DB
     end
 
     def each
-      while has_next
+      while move_next
         yield
       end
     end
 
-    abstract def has_next : Bool
-
-    # def read(t : T.class) : T
-    # end
+    abstract def move_next : Bool
 
     # list datatypes that must be supported form the driver
-    # implementors will override read_string
-    # users will call read(String) due to overloads read(T) will be a T
-    # TODO: unable to write unions (nillables)
-    {% for t in [String, UInt64] %}
+    # users will call read(String) or read?(String) for nillables
+    {% for t in DB::TYPES %}
+      abstract def read?(t : {{t}}.class) : {{t}}?
+
       def read(t : {{t}}.class) : {{t}}
-        read_{{t.name.underscore}}
+        read?({{t}}).not_nil!
       end
-
-      protected abstract def read_{{t.name.underscore}} : {{t}}
     {% end %}
-
-    # def read(t : String.class) : String
-    #   read_string
-    # end
-    #
-    # protected abstract def read_string : String
   end
 end

src/db/statement.cr

@@ -1,5 +1,7 @@
 module DB
   abstract class Statement
+    getter driver
+
     def initialize(@driver)
     end