iterate

iterate(x, f)でx, f(x), f(f(x)), ...と出します。unfoldでも実現可能だけど、めんどうなので。

template<typename T, typename U>
class cIterate : public cIterable<T> {
    T       current;
    U       func;
    bool    first;
    
public:
    cIterate(T x, U f) : current(x), func(f), first(true) { }
    
    bool exists_next() {
        if(first)
            first = false;
        else
            current = func(current);
        return true;
    }
    T value() const {
        return current;
    }
};

template<typename T, typename U>
shared_ptr<cIterable<T>> iterate(T x, U f) {
    return shared_ptr<cIterable<T>>(new cIterate<T,U>(x, f));
}

int main() {
    cout << takewhile([] (int n) { return n < 100; },
                iterate(1, [](int n) { return n * 2; })) << endl;
}

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