Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!cs.uoregon.edu!ns.uoregon.edu!milton!ogicse!pdxgate!parsely!percy!nosun!hilbert!jeff
From: jeff@hilbert.uucp (Jeff Freedman)
Newsgroups: comp.object
Subject: Re: Readability of Ada
Message-ID: <1991May3.181917.7553@hilbert.uucp>
Date: 3 May 91 18:19:17 GMT
References: <1991Apr25.170356.21237@odin.diku.dk> <jls.672698352@rutabaga> <1991Apr27.012355.29911@neon.Stanford.EDU>
Organization: Cypress Semiconductor Northwest, Beaverton Oregon
Lines: 47


>In article <jls.672698352@rutabaga> jls@rutabaga.Rational.COM (Jim Showalter)
>writes:
>   Consider the shapes example. Suppose that the given example goes
>   out in binary form, and arrives at my site, and I want to add a new
>   shape. Suppose that the initial shapes were limited to triangles and
>   squares. Suppose that I now add a Circle, which has a new method
>   defined for it that does NOT apply to triangles or squares and which
>   was never previously defined in the base class for shapes--radius.
>   This method returns the radius as some floating point number from 0
>   to whatever.
>(I used integers to save typing - ignore the details).
>   Now, I want to take a heterogeneous list of shapes, including triangles,
>   circles, and squares, and I want to iterate over the list and print
>   out all of the radii.

This is easy under the library which we're using.  I would be able to write,
without any changes to the Shapes class or methods, the following:

class Circle : public Shape
	{
	float radius;
public:
	..... (constructor, destructor, etc.)
	float get_radius() { return radius; }
	};

/*
 *	Print the radii of all the circles in a list of shapes.
 */

void Print_radii(Shape_list *shapes)
	{
					// Iterate through list.
	Shape_list_iterator next(shapes);
	Shape *each;
	while (next(each))
		{
					// A circle?  Print radius if so.
		Circle *circle = AS_A(each, Circle);
		if (circle)
			cout << circle->get_radius() << '\n';
		}
	}

Our library and environment were designed in-house, but I believe that ET++
and NIH provide similar facilities.