go - 为什么这不检查 nil in go 工作？

Question

在第一个代码示例中，“if pr != nil”行出现错误:

for sup, _ := range supervisorToColor {
        pr := emailToPerson[sup]
        // The line below causes the compilation error:
        // ./myprog.go:1046: missing condition in if statement
        // ./myprog.go:1046: pr != nil evaluated but not used
        if pr != nil 
        {   
          local := peopleOnFloor[pr.Email]
          sp := &Super{pr, local}
          names = append(names, sp) 
        }   
}   

如果我注释掉 nil 检查 if 语句，它编译正常:

for sup, _ := range supervisorToColor {
        pr := emailToPerson[sup]
        // if pr != nil 
        // {
          local := peopleOnFloor[pr.Email]
          sp := &Super{pr, local}
          names = append(names, sp) 
        // }
}   

起初我倾向于认为这是代码前面的一些语法错误，但当我注释掉这些行时它起作用的事实让我认为这是另外一回事。

emailToPerson 是 map[string]*Person 类型，其中 Person 是一个结构体

提前致谢。如果事实证明这是非常简单的事情，我们深表歉意。

Answer 1

左大括号需要与 if 在同一行:

if pr != nil { 

来自Go spec on semicolons :

The formal grammar uses semicolons ";" as terminators in a number of productions. Go programs may omit most of these semicolons using the following two rules:

1. When the input is broken into tokens, a semicolon is automatically inserted into the token stream immediately after a line's final token if that token is

   • an identifier
   • an integer, floating-point, imaginary, rune, or string literal
   • one of the keywords break, continue, fallthrough, or return
   • one of the operators and delimiters ++, --, ), ], or }

2. To allow complex statements to occupy a single line, a semicolon may be omitted before a closing ")" or "}".

这意味着您的代码等同于:

if pr != nil;
{
    // ...
}