为什么Go有一个“goto”声明 [英] Why does Go have a "goto" statement

问题描述

Google的Go语言是一种新语言。因此，我惊讶地发现它有'goto'声明。我总是被教导说'goto'陈述是过去的事情，它的邪恶阻碍了程序的实际流程。功能（或方法，如果你愿意的话）总是一个更好的控制流量的方法。

我必须缺少一些东西。为什么和何时使用'goto'是一个好主意？或者为什么Google包含它？

解决方案

当我们实际检查Gos源代码时（标准库 ），我们可以看到 goto s的实际应用情况。

例如，在 math / gamma.go 文件，使用goto语句：

  for x < 0 {
 if x> -1e-09 {
 goto small 
} 
 z = z / x 
 x = x + 1 
} 
 for x < 2 {
如果x < 1e-09 {
 goto small 
} 
z = z / x 
x = x + 1 
} 
 
 if x == 2 { 
 return z 
} 
 
x = x  -  2 
p =（（（（（x * _gamP [0] + _ gamP [1]）* x + _gamP [ 2]] * x + _gamP [3]）* x + _gamP [4]）* x + _gamP [5]）* x + _gamP [6] 
q =（（（（（（x * _gamQ [0] （x + _gamQ [5]）* x + _gamQ [5]）* x + _gamQ [6]）* x + _gamQ [2]）* x + _gamQ [3]）* _gamQ [7] 
返回z * p / q 
 
小：
如果x == 0 {
 return Inf（1）
} 
 return z /（（1 + Euler * x）* x）
} 
  

在这种情况下， goto 避免了引入另一个仅用于控制流的布尔变量，并在最后检查。 在这种情况下， goto 语句使得代码实际上更易于阅读和更容易遵循（与 goto you said。）

还要注意， goto 语句有一个非常具体的用例。关于goto的语言规范声明它不会跳过进入作用域（被声明）的变量，并且它可能不会跳转到其他（代码）块。

Google's Go language is a new language. Therefor I was surprised to find that it has a 'goto' statement. I've always been taught that 'goto' statements are a thing of the past and evil for it occludes the actual flow of a program. Function (or methods if you will) are always a better way of controlling flow.

I must be missing something. Why and when is using 'goto' a good idea? Or why did Google include it?

解决方案

When we actually check Gos source code (the standard library), we can see where gotos are actually well applied.

For example, in the math/gamma.go file, the goto statement is used:

  for x < 0 {
    if x > -1e-09 {
      goto small
    }
    z = z / x
    x = x + 1
  }
  for x < 2 {
    if x < 1e-09 {
      goto small
    }
    z = z / x
    x = x + 1
  }

  if x == 2 {
    return z
  }

  x = x - 2
  p = (((((x*_gamP[0]+_gamP[1])*x+_gamP[2])*x+_gamP[3])*x+_gamP[4])*x+_gamP[5])*x + _gamP[6]
  q = ((((((x*_gamQ[0]+_gamQ[1])*x+_gamQ[2])*x+_gamQ[3])*x+_gamQ[4])*x+_gamQ[5])*x+_gamQ[6])*x + _gamQ[7]
  return z * p / q

small:
  if x == 0 {
    return Inf(1)
  }
  return z / ((1 + Euler*x) * x)
}

The goto in this case saves us from introducing another (boolean) variable used just for control-flow, checked for at the end. In this case, the goto statement makes the code actually better to read and easier follow (quite in contrary to the argument against goto you mentioned).

Also note, that the goto statement has a very specific use-case. The language specification on goto states that it may not jump over variables coming into scope (being declared), and it may not jump into other (code-)blocks.

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