[tgpl]go匿名函数
[tgpl]go匿名函数
0. 定义
匿名函数顾名思义是没有名字的函数,
Named functions can be declared only at the package level, but we can use a function literal to denote a function value within any expression.
1. 最简单的例子Map
strings.Map(func(r rune) rune { return r + 1 }, "HAL-9000")
strings 包里面的Map函数,第一个参数是mapping,一个函数对象。直接用匿名函数操作很完美。
2. squares
gopl.io/ch5/squares
// squares returns a function that returns
// the next square number each time it is called.
func squares() func() int {
var x int
return func() int {
x++
return x * x
} }
func main() {
f := squares()
fmt.Println(f()) // "1"
fmt.Println(f()) // "4"
fmt.Println(f()) // "9"
fmt.Println(f()) // "16"
}
很有意思,suqares函数返回一个匿名函数,里面有个local变量,匿名函数能访问到那个local变量,这点就很神奇了。
原文是
More importantly, functions defined in this way have access to the entire lexical environment, so the inner function can refer to variables from the enclosing function
如果你定义一个g,里面的变量x也是独立的,跟f的x不是一个。
g := squares()
fmt.Println(g())
fmt.Println(g())
fmt.Println(g())
fmt.Println(g())
3. defer 里面调用匿名函数
func bigSlowOperation() {
defer trace("bigSlowOperation")() // don't forget the extra parentheses
// ...lots of work...
time.Sleep(10 * time.Second) // simulate slow operation by sleeping
}
func trace(msg string) func() {
start := time.Now()
log.Printf("enter %s", msg)
return func() { log.Printf("exit %s (%s)", msg, time.Since(start)) }
}
bigSlowOperation里面加了个defer trace,而trace返回了一个匿名函数,so 匿名函数里面的local变量对该匿名函数是可见的,所以time.Since能访问到start,也就算出了整个操作的时间。
from
引用tgpl ch5。