Go语言编译原理之变量捕获

package main
import (
	"fmt"
)
func main() {
	a := 1
	b := 2
	go func() {
		//在闭包里对a或b进行了重新赋值，也会改变引用方式
		fmt.Println(a, b)
	}()
	a = 666
}

go tool compile -m=2 main.go | grep capturing

func adder() func(int) int {//累加器
	sum := 0 //地址引用
	return func(v int) int {
		sum += v
		return sum
	}
}
func main() {
	a := adder()
	for i:=0;i<10;i++{
		fmt.Printf("0 + 1 + ... + %d = %d\n", i, a(i))
	}
}

编译入口文件：src/cmd/compile/main.go -> gc.Main(archInit)
// Phase 4: Decide how to capture closed variables.（决定如何捕获闭包变量）
// This needs to run before escape analysis,
// because variables captured by value do not escape.（变量捕获应该在逃逸分析之前进行，因为值类型的变量捕获，不会进行逃逸分析）
	timings.Start("fe", "capturevars")
	for _, n := range xtop {
		if n.Op == ODCLFUNC && n.Func.Closure != nil { //函数需要是闭包类型
			Curfn = n
			capturevars(n)
		}
	}
	capturevarscomplete = true

func capturevars(xfunc *Node) {
	......
	clo := xfunc.Func.Closure
	cvars := xfunc.Func.Cvars.Slice()
	out := cvars[:0]
	for _, v := range cvars {
		......
		out = append(out, v)
		......
		outer := v.Name.Param.Outer
		outermost := v.Name.Defn
		// out parameters will be assigned to implicitly upon return.
		if outermost.Class() != PPARAMOUT && !outermost.Name.Addrtaken() && !outermost.Name.Assigned() && v.Type.Width <= 128 {
			v.Name.SetByval(true)
		} else {
			outermost.Name.SetAddrtaken(true)
			outer = nod(OADDR, outer, nil)
		}
		......
		outer = typecheck(outer, ctxExpr)
		clo.Func.Enter.Append(outer)
	}
	xfunc.Func.Cvars.Set(out)
	lineno = lno
}