Anonymous functions

What are anonymous functions? A description is a function that has not been given a name, for example:

package main

import (
	"fmt"
)

func main(a) {
    // Anonymous function definition method 1
	func (s string){
		fmt.Printf("Anonymous function :%s\n",s)
	}("Definition Method 1")

    // Anonymous function definition method 2
	fn:=func (s string){
		fmt.Printf("Anonymous function :%s\n",s)
	}
	fn("Definition Mode 2")}Copy the code

closure

A closure is actually an instance of a function, that is, a structure that exists in memory. In terms of implementation, an anonymous function that does not capture free variables can be implemented as a function pointer, or directly inline to the call point. If it does capture free variables, it will be a closure.

Closures are meant to contain both the function pointer and the environment. In compilation optimization, closures that do not capture free variables can be optimized into ordinary functions without assigning closure structures, a compilation technique known as function jump.

Closure = function + reference environment

package main

import (
	"fmt"
)

func main(a) {
    // c copies the closure copy
	c:=Closure()
	c()	// Call the closure
	c() // Call the closure
    
	// C2 copies the new closure
	c2:=Closure()
	c2() // Call the closure
}
/ * closure * /
func Closure(a) func(a){
	i:=1
	return func(a) {
		i++
		fmt.Printf("The closure, I = % d \ n",i)
	}
}
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Output:

Closure, I =2 closure, I =3 closure, I =2Copy the code

Escape analysis

The GO language recognizes the scope of variables through Escape Analyze and automatically allocates variables on the heap. Allocating closure environment variables on the heap is the foundation of Go’s implementation of closures.

The above code can be analyzed with the following command:

go build --gcflags=-m main.go
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Output:

# command-line-arguments
./main.go:23:13: inlining call to fmt.Printf
./main.go:20:2: moved to heap: i
./main.go:21:9: func literal escapes to heap
./main.go:23:14: i escapes to heap
./main.go:23:13: []interface{} {... } does not escape <autogenerated>:1: .this does not escape

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**./main.go:23:14: I escapes to heap**