如何在类成员初始化中使用boost累加器quantile_probability？

Question

Boost累加器有一个不幸的怪癖，当在类内部使用时，api接口的行为会有所不同。

我试图在类中使用Boost累加器quantile_probability，但是我想不出如何使它工作。

这个问题类似于这个问题：Can boost accumulators be used as class members

  #include <boost/accumulators/accumulators.hpp>
  #include <boost/accumulators/statistics/stats.hpp>
  #include <boost/accumulators/statistics/weighted_p_square_cumul_dist.hpp>
  #include <boost/accumulators/statistics/weighted_p_square_quantile.hpp>
  #include <boost/accumulators/statistics/parameters/quantile_probability.hpp>

  namespace ba = boost::accumulators;

  typedef ba::accumulator_set<int64_t, ba::stats<ba::tag::weighted_p_square_quantile>, int64_t> accumulator_t;

  struct Foo {
      accumulator_t myAcc(ba::quantile_probability = 0.90);  // Doesn't work. ERROR: ‘ba::quantile_probability’ is not a type
  };

  accumulator_t acc(ba::quantile_probability = 0.90);   // I just fine!

Answer 1

accumulator_t myAcc(中的方括号被解析为成员函数，在这种情况下，这是定义一个变量为ba::qunatile_probability的函数。但那不是一种类型，所以它失败了。

您需要用=或{编写初始化程序，或者将其写入构造函数的初始化程序列表中。

struct Foo {
    // One of these
    accumulator_t myAcc = accumulator_t(ba::quantile_probability = 0.90);

    accumulator_t myAcc{ba::quantile_probability = 0.90};
    
    accumulator_t myAcc;
    Foo() : myAcc(ba::quantile_probability = 0.90) {}
};