Ada 继承和多态小例

三个文件，一条命令构建。

-- 文件：oo.ads

package OO is
	type Object is tagged record
		X : Float;
		Y : Float;
	end record;

	function Area (Obj : Object) return Float;

	type Point is new Object with null record;

	type Circle is new Object with record
		Raduis : Float;
	end record;

	overriding function Area (Cir : Circle) return Float;

	procedure Put_Area (Obj : Object'Class);
end OO;

-- 文件：oo.adb

with Ada.Text_IO;
use Ada.Text_IO;

package body OO is
	function Area(Obj : Object) return Float is
	begin
		return 0.0;
	end Area;

	function Area (Cir : Circle) return Float is
	begin
		return 3.24 * Cir.Raduis ** 2;
	end Area;

	procedure Put_Area (Obj : Object'Class) is
	begin
		Put_Line (Area(Obj)'Image);
	end Put_Area;
end OO;

--文件：main.adb

with Ada.Text_IO;
use Ada.Text_IO;
with OO;

procedure Main is
	use OO;
	
	Obj : Object := (0.0, 0.0);
	Poi	: Point := (0.0, 0.0);
	C : Circle := (0.0, 0.0, 1.0);
begin
	Put(Obj.X'Image);
	Put(Obj.Y'Image);
	New_Line;
	Put_Area(Obj);
	Put_Area(Poi);
	Put_Area(C);
end Main;

#构建
gnatmake main.adb