staticpoly.cpp

C++ Templates 完全导引范例

/* The following code example is taken from the book
 * "C++ Templates - The Complete Guide"
 * by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley, 2002
 *
 * (C) Copyright David Vandevoorde and Nicolai M. Josuttis 2002.
 * Permission to copy, use, modify, sell and distribute this software
 * is granted provided this copyright notice appears in all copies.
 * This software is provided "as is" without express or implied
 * warranty, and with no claim as to its suitability for any purpose.
 */
#include "statichier.hpp"
#include <vector>

// draw any GeoObj
template <typename GeoObj>
void myDraw (GeoObj const& obj)
{
    obj.draw();    // call draw() according to type of object
}

// process distance of center of gravity between two GeoObjs
template <typename GeoObj1, typename GeoObj2>
Coord distance (GeoObj1 const& x1, GeoObj2 const& x2)
{
    Coord c = x1.center_of_gravity() - x2.center_of_gravity();
    return c.abs();  // return coordinates as absolute values
}

// draw homogeneous collection of GeoObjs
template <typename GeoObj>
void drawElems (std::vector<GeoObj> const& elems)
{
    for (unsigned i=0; i<elems.size(); ++i) {
        elems[i].draw();    // call draw() according to type of element
    }
}

int main()
{
    Line l;
    Circle c, c1, c2;

    myDraw(l);        // myDraw<Line>(GeoObj&) => Line::draw()
    myDraw(c);        // myDraw<Circle>(GeoObj&) => Circle::draw()

    distance(c1,c2);  // distance<Circle,Circle>(GeoObj1&,GeoObj2&)
    distance(l,c);    // distance<Line,Circle>(GeoObj1&,GeoObj2&)

    // std::vector<GeoObj*> coll;    // ERROR: no heterogeneous
                                   //      collection possible
    std::vector<Line> coll;   // OK: homogeneous collection possible
    coll.push_back(l);        // insert line
    drawElems(coll);          // draw all lines
}