问题描述
在之后应用 map、flatmap 等函数时，使用 withFilter 而不是 filter 总是更高效吗?
Is it always more performant to use withFilter instead of filter, when afterwards applying functions like map, flatmap etc.?
为什么只支持 map、flatmap 和 foreach?(预期的功能，如 forall/exists 以及)
Why are only map, flatmap and foreach supported? (Expected functions like forall/exists as well)
推荐答案
来自 :
注意:c filter p 和 c withFilter p 的区别在于前者创建一个新的集合，而后者只限制域后续的map、flatMap、foreach 和withFilter 操作.
所以 filter 将获取原始集合并生成一个新集合，但是 withFilter 将非严格地(即懒惰地)将未过滤的值传递给以后的 map/flatMap/withFilter 调用，保存第二次通过(过滤的)集合.因此在传递到这些后续方法调用时会更有效率.
So filter will take the original collection and produce a new collection, but withFilter will non-strictly (i.e. lazily) pass unfiltered values through to later map/flatMap/withFilter calls, saving a second pass through the (filtered) collection. Hence it will be more efficient when passing through to these subsequent method calls.
事实上，withFilter 是专门为处理这些方法链而设计的，这就是理解的脱糖.不需要其他方法(例如forall/exists)，因此它们没有被添加到FilterMonadic返回类型中>withFilter.
In fact, withFilter is specifically designed for working with chains of these methods, which is what a for comprehension is de-sugared into. No other methods (such as forall/exists) are required for this, so they have not been added to the FilterMonadic return type of withFilter.
这篇关于用过滤器代替过滤器的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！