STL - 容器 - 运行期指定排序准则

#include <set>

using namespace std;

// type for runtime sorting criterion
class RuntimeCmp 
{
public:
    enum cmp_mode { normal, reverse };
private:
    cmp_mode mode;
public:
    // constructor for sorting criterion
    // - default criterion uses value normal
    RuntimeCmp(cmp_mode m = normal) : mode(m) { }
    // comparison of elements
    // - member function for any element type
    template <typename T>
    bool operator() (const T& t1, const T& t2) const 
    {
        return mode == normal ? t1<t2
            : t2<t1;
    }
    // comparison of sorting criteria
    bool operator== (const RuntimeCmp& rc) const 
    {
        return mode == rc.mode;
    }
};

// type of a set that uses this sorting criterion
typedef set<int, RuntimeCmp> IntSet;

#include <iostream>
#include <set>
#include <algorithm>
#include <iterator>
#include <functional>
#include "SetTest.h"
#include "../../Core/RuntimeCmp.hpp"
#include "../../Core/print.hpp"

using namespace std;

void SetTest::runtimeCompare()
{
    // create, fill, and print set with normal element order
    // - uses default sorting criterion
    IntSet coll1 = { 4, 7, 5, 1, 6, 2, 5 };
    PRINT_ELEMENTS(coll1, "coll1: ");

    // create sorting criterion with reverse element order
    RuntimeCmp reverse_order(RuntimeCmp::reverse);

    // create, fill, and print set with reverse element order
    IntSet coll2(reverse_order);
    coll2 = { 4, 7, 5, 1, 6, 2, 5 };
    PRINT_ELEMENTS(coll2, "coll2: ");

    // assign elements AND sorting criterion
    coll1 = coll2;
    coll1.insert(3);
    PRINT_ELEMENTS(coll1, "coll1: ");

    // just to make sure...
    if (coll1.value_comp() == coll2.value_comp()) 
    {
        cout << "coll1 and coll2 have the same sorting criterion"
            << endl;
    }
    else 
    {
        cout << "coll1 and coll2 have a different sorting criterion"
            << endl;
    }
}

void SetTest::run()
{
    printStart("runtimeCompare()");
    runtimeCompare();
    printEnd("runtimeCompare()");
}