Method pop_front

smallthinker/common/sampling.cpp:55–63

    }

    T pop_front() {
        if (sz == 0) {
            throw std::runtime_error("ring buffer is empty");
        }
        T value = data[first];
        first = (first + 1) % capacity;
        sz--;
        return value;
    }

    const T & rat(size_t i) const {
        if (i >= sz) {