"=>" 在scala 中的意思

最新推荐文章于 2023-06-01 17:17:24 发布

最新推荐文章于 2023-06-01 17:17:24 发布 · 239 阅读

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本文探讨了Scala编程语言中箭头符号的不同用途，包括匿名函数定义、函数类型声明、by-name参数以及在case语句中的应用。此外，还介绍了这些概念与数学中的蕴含概念之间的联系。

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

1、匿名函数定义，左边是参数右边是函数实现体（x: Int）=>{}

2、函数类型的声明,左边是参数类型，右边是方法返回值类型 (Int)=>(Int)

3、 By-name-parameter f（p :=>Int）

4、 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

=> 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 for Function<n>[A[,B,...],T], that is, a function that takes parameters of type A[,B...], and returns a value of type T.（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 type Unit, 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）