斯卡拉的两套联盟 [英] Union of two sets in Scala
问题描述
从链接这里的问题中,我发现了这个在Scala中实现的联盟:
def union(a:Set,b:Set):Set = i => a(i)|| b(i)
Set是一个类型的函数:
type Set = Int =>布尔
现在我明白在Scala中,函数从Int到Boolean映射到这里,而且我进一步了解如何执行此语句:
a(i)|| b(i)
但我不明白的是'我'在这里是什么。它从何而来?当它找到集合之间的匹配时,它返回true,如果确实如此,我在哪里过滤它? 假设我们有一个名为 SoSet
的对象,它由
object SoSet {
类型Set = Int =>布尔
val a:Set = ???
val b:Set = ???
def isItem(item:Int)= a(item)|| b(项目)
}
由
Int =>给出。布尔
,它是 Set
。到现在为止还挺好。
但是现在我们只想返回函数 isItem
(即一个集
)。
因此,我们定义 union
函数(现在没有参数,我们稍后会添加它)。
object SoSet {
// ..
def union:Set = isItem //返回函数isItem
}
现在让我们重构 isItem
转换为匿名函数。
object SoSet {
// ..
def union:Set = {
(item:Int)=>一个(item)|| b(物品)
}
}
让我们移动从
为对象SoSet
设置a和b 项目
到 i
。
object SoSet {
type Set = Int =>布尔
def union(a:Set,b:Set):Set =(i:Int)=> a(i)|| b(i)
}
更新
val s1 =设置(1,2,3)
val s2 =设置(2,3,4)
val s3 = union(s1,s2)//返回函数.. Int =>布尔=< function1>
s3(2)//调用函数&检查工会中是否存在2
From the question linked here, I found this implementation of Union in Scala:
def union(a: Set, b: Set): Set = i => a(i) || b(i)
And Set is a function of type:
type Set = Int => Boolean
Now I understand that in Scala, a function is mapped from Int to Boolean here, and I further understand how this statement is executed:
a(i) || b(i)
But what I don't understand is what is 'i' here. Where does it come from? And when it finds a match between to sets, it returns true, if it indeed does, where do I filter it?
Let say we have object called SoSet
given by
object SoSet {
type Set = Int => Boolean
val a : Set = ???
val b : Set = ???
def isItem(item : Int) = a(item) || b(item)
}
The signature of isItem
is given by Int => Boolean
which is a Set
. So far so good.
But now we just want to return the function isItem
(i.e. a Set
).
So lets define union
function for this (There are no parameters right now. We will add it later).
object SoSet {
//..
def union : Set = isItem // returns the function isItem
}
Now lets refactor the isItem
into a anonymous function.
object SoSet {
//..
def union : Set = {
(item : Int) => a(item) || b(item)
}
}
Lets move Set a and b
from object SoSet
to parameters of def union
. Refactor item
to i
.
object SoSet {
type Set = Int => Boolean
def union(a : Set, b : Set) : Set = (i : Int) => a(i) || b(i)
}
UPDATE
val s1 = Set(1, 2, 3)
val s2 = Set(2, 3, 4)
val s3 = union(s1, s2) // returns the function.. Int => Boolean = <function1>
s3(2) // invokes the function & checks if 2 is present in the union
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