RX 中没有主题的反馈循环 [英] Feedback loop without Subject in RX

问题描述

我有以下运动方程

move = target_position - position
position = position + move

其中 target_position 是一个流，位置初始化为零.我想有一个职位流.我尝试过这样的事情(在 rx 伪代码中)

where target_position is a stream and position is initialized at zero. I would like to have a stream of position. I have tried something like this (in rx pseudo code)

moves = Subject()
position = moves.scan(sum,0)
target_position.combine_latest(position,diff).subscribe( moves.on_next)

它有效，但我读过应该避免使用主题.是否可以在没有 Subject 的情况下计算位置流?

It works but I have read that using Subject should be avoided. Is it possible to compute the position stream without Subject?

在python中，完整的实现是这样的

In python the full implementation looks like this

from pprint import pprint 
from rx.subjects import Subject

target_position = Subject()

moves = Subject()

position = moves.scan(lambda x,y: x+y,0.0)

target_position\
    .combine_latest(position,compute_next_move)\
    .filter(lambda x: abs(x)>0)\
    .subscribe( moves.on_next)

position.subscribe( lambda x: pprint("position is now %s"%x))

moves.on_next(0.0)
target_position.on_next(2.0)
target_position.on_next(3.0)
target_position.on_next(4.0)

推荐答案

你可以使用 扩展运算符

targetPosition.combineLatest(position, (target, current) => [target, current])
  .expand(([target, current]) => {
    // if you've reached your target, stop
    if(target === current) {
      return Observable.empty()
    }
    // otherwise, calculate the new position, emit it
    // and pump it back into `expand`
    let newPosition = calcPosition(target, current);
    return Observable.just(newPosition)
  })
  .subscribe(updateThings);

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