目前知道的基本和匿名函数定义和函数类型声明有关,以及在case语句中的使用
case
语句中
case x => y
不过stackoverflow 上关于这方面的讨论挺多的,故在此记录一下
比如来自 http://stackoverflow.com/questions/6951895/what-does-and-mean-in-scala 的一位的回复:
=> has several meanings in Scala, all related to its mathematical meaning as implication.
-
In a value, it introduces a function literal, or lambda. e.g. the bit inside the curly braces in
List(1,2,3).map { (x: Int) => x * 2 }(匿名函数定义)
-
In a type, with symbols on both sides of the arrow (e.g.
A => T
,(A,B) => T
,(A,B,C) => T
, etc.) it's sugar forFunction<n>[A[,B,...],T]
, that is, a function that takes parameters of typeA[,B...]
, and returns a value of typeT
.(函数类型定义)-
Empty parens on the left hand side (e.g.
() => T
) indicate that the function takes no parameters (also sometimes called a "thunk"); -
Empty parens on the right hand side denote that it returns
()
—the sole value of typeUnit
, whose name can also be written()
—confused yet? :)A function that returns Unit is also known as a procedure, normally a method that's called only for its side effect.
-
-
In the type declaration for a method or function parameter, with no symbol on the left hand side (e.g.
def f(param: => T)
) it's a "by-name parameter", meaning that is evaluated every time it's used within the body of the function, and not before. Ordinary "by-value" parameters are evaluated before entry into the function/method.(函数类型定义) -
In a
case
clause, they separate the pattern (and optional guard) from the result expression, e.g.case x => y
.(case 语句)
http://stackoverflow.com/questions/6951895/what-does-and-mean-in-scala
http://stackoverflow.com/questions/7888944/scala-punctuation-aka-symbols-and-operators