Scala forall 示例？
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Scala forall example?
提问by Jus12
I tried Google search and could not find a decent forallexample. What does it do? Why does it take a boolean function?
我尝试了谷歌搜索，但找不到像样的forall例子。它有什么作用？为什么它需要一个布尔函数？
Please point me to a reference (except the Scaladoc).
请给我一个参考（Scaladoc 除外）。
回答by dhg
The forallmethod takes a function pthat returns a Boolean. The semantics of forallsays: return trueif for every xin the collection, p(x)is true.
该forall方法采用一个p返回布尔值的函数。语义forall说：true如果对于x集合中的每个都返回，p(x)则为真。
So:
所以：
List(1,2,3).forall(x => x < 3)
means: trueif 1, 2, and 3 are less than 3, falseotherwise. In this case, it will evaluate to falsesince it is not the case all elements are less than 3: 3 is not less than 3.
意思是：true如果1、2、3都小于3，false否则。在这种情况下，它将评估为，false因为并非所有元素都小于 3：3 不小于 3。
There is a similar method existsthat returns trueif there is at least oneelement xin the collection such that p(x)is true.
如果集合中至少有一个元素为真exists，true则有一个类似的方法返回。xp(x)
So:
所以：
List(1,2,3).exists(x => x < 3)
means: trueif at least one of1, 2, and 3 is less than 3, falseotherwise. In this case, it will evaluate to truesince it is the case some element is less than 3: e.g. 1 is less than 3.
意思是：true如果1、2、3中至少有一个小于3，false否则。在这种情况下，它将评估为，true因为某些元素小于 3：例如 1 小于 3。
回答by James Raitsev
A quick example of how you can play with this function using a Scalascript.
一个关于如何使用Scala脚本玩这个函数的快速示例。
create a myScript.scalafile with
创建一个myScript.scala文件
println(args.forall(p => (p.equals("a"))))
and call it with
并调用它
scala myScript.scala a a a // true
scala myScript.scala a b c // false
回答by Johnny
Scala's forallis also a great tool to do something like applying logical andto a list of boolean values with the early exist:
Scalaforall也是一个很好的工具，可以执行诸如将逻辑和布尔值列表应用于早期存在的操作：
val evalResults: List[Boolean] = List(evaluateFunc1(), evaluateFunc2(), evaluateFunc3(), evaluateFunc4(), evaluateFunc5())
evalResults.forall(result => result == true)
