go - 初始化周期错误

Question

我有自动生成的代码。简化版:

package main

// begin of A
func main(){
    ParseReader("x")
}
func parseInclude(fileName string) (interface{}, error) {
    got, _ := ParseReader(fileName)
    return got, nil
}
// end of A
type grammar struct {
    pos   int
    run  func(*parser) (interface{}, error)
}
var g = &grammar{
    pos:  1,
    run: (*parser).callonIncludeOp1,
}

type parser struct {
    filename string
    cur      current
}
func (p *parser) callonIncludeOp1() (interface{}, error) {
    return p.cur.onIncludeOp1("x")
}
func (p *parser) parse(g *grammar) (val interface{}, err error) {
    return g.pos, nil
}

type current struct {
    pos  int 
}
// B
func (c *current) onIncludeOp1(qfilename interface{}) (interface{}, error) {
    got, _ := parseInclude("x")
    return got, nil
}

func ParseReader(filename string) (interface{}, error) {
    p := &parser{ filename: filename }
    return p.parse(g)
}

编译后出现错误

./prog.go:19: initialization loop:
    /home/gCDfp4/prog.go:19 g refers to
    /home/gCDfp4/prog.go:25 (*parser).callonIncludeOp1 refers to
    /home/gCDfp4/prog.go:36 (*current).onIncludeOp1 refers to
    /home/gCDfp4/prog.go:7 parseInclude refers to
    /home/gCDfp4/prog.go:41 ParseReader refers to
    /home/gCDfp4/prog.go:19 g

我需要在语法上进行递归调用，因为我有预处理器运算符“#include”来解析其他文件。

因为它是自动生成的代码，所以我只能修改 block A 或函数 B 中的代码。

我怎样才能打破初始化周期？

Answer 1

这是 package initialization 的结果其中:

Dependency analysis does not rely on the actual values of the variables, only on lexical references to them in the source, analyzed transitively.

For instance, if a variable x's initialization expression refers to a function whose body refers to variable y then x depends on y.

As in: "A reference to a variable or function is an identifier denoting that variable or function."

你的 example in a playground返回更直接的东西:

tmp/sandbox395359317/main.go:21: initialization loop:
    prog.go:21 g refers to
    prog.go:28 (*parser).callonIncludeOp1 refers to
    prog.go:21 g

有techniques in Go for loose coupling ，例如接口(interface)。

举个例子(不是最优的，但至少打破了初始化循环)，你可以在//A中添加:

type parseIncluder interface {
    parseInclude(fileName string) (interface{}, error)
}

func (c *current) parseInclude(fileName string) (interface{}, error) {
    return parseInclude(fileName)
}

而在 //B 中，对 parseInclude() 的调用变为:

got, _ := c.cParseIncluder().parseInclude("x")

参见 Go plaground然后单击运行:不再有初始化循环。

---

OP Red Skotina使用了不同的方法 package init() function :

var gProxy grammar

func init() { gProxy = g }
func parseInclude(fileName string) (interface{}, error) {
    got, _ := ParseReaderProxy(fileName)
    return got, nil
}
func ParseReaderProxy(filename string) (interface{}, error) {
    p := &parser{filename: filename}
    return p.parse(gProxy)
}