SCIP in C++11 ― 2.2.1節 その3

可変長引数：問題2.20

C++11の可変長引数テンプレートは、再帰と組み合わせるとかなり強力だなあ。

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//---------abstraction barrier---------

template<typename ...Arguments>

const List sameParity(const int arg1, const Arguments& ...args)

{

    const int parity(arg1%2);

    function<List(List)> filterSameParity;

    filterSameParity=[parity,&filterSameParity]

        (const List& numList){

        if(isNull(numList)){return(numList);}

        if(parity!=value<int>(car(numList))%2){

            return(filterSameParity(cdr(numList)));

        }

        return(cons(car(numList),filterSameParity(cdr(numList))));

    };

    return(cons(arg1,filterSameParity(makeList(args...))));

}

int main(int argc, char** argv)

{

    auto list1(sameParity(1,2,3,4,5,6,7));

    cout<<"(same-parity 1 2 3 4 5 6 7)="<<listString(list1)<<endl;

    auto list2(sameParity(2,3,4,5,6,7));

    cout<<"(same-parity 2 3 4 5 6 7)="<<listString(list2)<<endl;

}

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出力

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(same-parity 1 2 3 4 5 6 7)=(1 3 5 7)

(same-parity 2 3 4 5 6 7)=(2 4 6)