去golang，语法错误：意想不到的++，期待： [英] Go golang, syntax error: unexpected ++, expecting :

问题描述

  func test（args ... string）{
 var msg map [string] interface {} 
 
i：= 0 
 msg [product] = args [i ++] 
 msg [key] = args [i ++] 
 msg [signature] = args [i ++] 
 msg [string_to_sign ] = args [i ++] 
} 
 
 go build utils.go 
  

编译后，我收到错误消息：

  ./utils.go:28：语法错误：意外的++，期望：
 ./utils.go:28：缺少标签后的语句
 ./utils.go:29：语法错误：意外++，期待：
 ./utils.go:30 ：语法错误：意外++，期待：
 ./utils.go:31：语法错误：意外++，期待：
 ./utils.go:36：语法错误：意外++，期望：
 ./utils.go:37：语法错误：意外++，期待：
  

<为什么我不能把i ++放在切片的索引中？在切片的索引中是否有任何限制？

解决方案

常见问题解答

为什么是++和 - 语句而不是表达式？为什么postfix，
不是前缀？

如果没有指针算术，前缀和后缀
增量运算符的便利值会下降。通过将它们从表达式
全部删除，表达式语法被简化并且乱七八糟的
以评估++和 - （考虑f（i ++）和
p [i] = q [++ i]）也被淘汰。简化是
显着。至于后缀与前缀，两者都可以正常工作，但
后缀版本更传统;坚持前缀与
一起产生了STL，一个语言库，其名称中含有讽刺意味的是
后缀增量。

Go编程语言规范

++和 - 语句将它们的操作数增加或减少
无类型常量1.与赋值一样，操作数必须是
addressable或map index表达式。 =表达式（++| - ）。

以下赋值语句在语义上是等效的：

  IncDec语句赋值
 x ++ x + = 1 
 x-- x  -  = 1 
  

Write，

  func test args ... string）{
 var msg map [string] interface {} 
i：= 0 
 msg [product] = args [i] 
 i ++ 
 msg [key] = args [i] 
 i ++ 
 msg [signature] = args [i] 
 i ++ 
 msg [string_to_sign] = args [ i] 
} 
  

在您的特定情况下，它简化为

$ b $

  func test（args ... string）{
 var msg map [string] interface {} 
 msg [产品] = args [0] 
 msg [key] = args [1] 
 msg [signature] = args [2] 
 msg [string_to_sign] = args [3] 
} 
  

  func test(args ...string) {
    var msg map[string] interface{}

    i := 0
    msg["product"] = args[i++]
    msg["key"] = args[i++]
    msg["signature"] = args[i++]
    msg["string_to_sign"] = args[i++]
  }

  go build utils.go

after compile, I get the error message

    ./utils.go:28: syntax error: unexpected ++, expecting :
    ./utils.go:28: missing statement after label
    ./utils.go:29: syntax error: unexpected ++, expecting :
    ./utils.go:30: syntax error: unexpected ++, expecting :
    ./utils.go:31: syntax error: unexpected ++, expecting :
    ./utils.go:36: syntax error: unexpected ++, expecting :
    ./utils.go:37: syntax error: unexpected ++, expecting :

why can't I put i++ in index of slice? is there any limitation in index of slice?

解决方案

Go Frequently Asked Questions (FAQ)

Why are ++ and -- statements and not expressions? And why postfix, not prefix?

Without pointer arithmetic, the convenience value of pre- and postfix increment operators drops. By removing them from the expression hierarchy altogether, expression syntax is simplified and the messy issues around order of evaluation of ++ and -- (consider f(i++) and p[i] = q[++i]) are eliminated as well. The simplification is significant. As for postfix vs. prefix, either would work fine but the postfix version is more traditional; insistence on prefix arose with the STL, a library for a language whose name contains, ironically, a postfix increment.

The Go Programming Language Specification

IncDec statements

The "++" and "--" statements increment or decrement their operands by the untyped constant 1. As with an assignment, the operand must be addressable or a map index expression.

IncDecStmt = Expression ( "++" | "--" ) .

The following assignment statements are semantically equivalent:

IncDec statement    Assignment
x++                 x += 1
x--                 x -= 1

Write,

func test(args ...string) {
    var msg map[string]interface{}
    i := 0
    msg["product"] = args[i]
    i++
    msg["key"] = args[i]
    i++
    msg["signature"] = args[i]
    i++
    msg["string_to_sign"] = args[i]
}

Which, in your particular case, simplifies to,

func test(args ...string) {
    var msg map[string]interface{}
    msg["product"] = args[0]
    msg["key"] = args[1]
    msg["signature"] = args[2]
    msg["string_to_sign"] = args[3]
}

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