Contract Programming - D Programming Language
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Keywords: D programming language

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# Contract Programming

#### Contract Programming Dersi Problem Çözümleri

The `unittest` block can be implemented trivially by copying the checks that are already written in `main()`. The only addition below is the test for the case when the second team wins:

    int addPoints(int goals1, int goals2,
                  ref int points1, ref int points2)
    in {
        assert(goals1 >= 0);
        assert(goals2 >= 0);
        assert(points1 >= 0);
        assert(points2 >= 0);

    } out (result) {
        assert((result >= 0) && (result <= 2));

    } do {
        int winner;

        if (goals1 > goals2) {
            points1 += 3;
            winner = 1;

        } else if (goals1 < goals2) {
            points2 += 3;
            winner = 2;

        } else {
            ++points1;
            ++points2;
            winner = 0;
        }

        return winner;
    }

    unittest {
        int points1 = 10;
        int points2 = 7;
        int winner;

        // First team wins
        winner = addPoints(3, 1, points1, points2);
        assert(points1 == 13);
        assert(points2 == 7);
        assert(winner == 1);

        // Draw
        winner = addPoints(2, 2, points1, points2);
        assert(points1 == 14);
        assert(points2 == 8);
        assert(winner == 0);

        // Second team wins
        winner = addPoints(0, 1, points1, points2);
        assert(points1 == 14);
        assert(points2 == 11);
        assert(winner == 2);
    }

    void main() {
        // ...
    }

Expression-based contracts can be useful for this function:

    int addPoints(int goals1, int goals2,
                  ref int points1, ref int points2)
    in (goals1 >= 0)
    in (goals2 >= 0)
    in (points1 >= 0)
    in (points2 >= 0)
    out (result; (result >= 0) && (result <= 2)) {
        // ...
    }

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