Golang 关于语法的一点疑惑

資深大佬 : linvon 3

         type Int struct {   v int  }   // 不合法  for i := Int{v:0}; i.v < 10; i.v ++ {}   // 合法 1         i := Int{v:0}         for ; i.v < 10; i.v ++ {} // 合法 2         for i := 0; i < 10; i++ {}

也是网上冲浪的时候看到有人抛出的这段代码，循环体的初始化条件中不能直接赋值结构体使用。如果说赋值结构体是无返回值表达式的话，那为什么直接赋值 0 可以？
没有理解到为什么会有这种限制，有没有老哥指点一二？感觉自己在学习过程中漏掉了什么东西

大佬有話說 (5)

資深大佬 : elvodn

for i := (Int{v:0}); i.v < 10; i.v++ {}

主資深大佬 : linvon

@elvodn 感谢

資深大佬 : elvodn

原因在这里 https://golang.org/ref/spec#Semicolons

資深大佬 : rayhy

不是特别理解上说的原因，是指这条规则吗?

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

怎么理解呢？

資深大佬 : elvodn

@rayhy
@szzhiyang
@ScepterZ
@linvon

我理解错了，原因是这一条 https://golang.org/ref/spec#Composite_literals
A parsing ambiguity arises when a composite literal using the TypeName form of the LiteralType appears as an operand between the keyword and the opening brace of the block of an “if”, “for”, or “switch” statement, and the composite literal is not enclosed in parentheses, square brackets, or curly braces. In this rare case, the opening brace of the literal is erroneously parsed as the one introducing the block of statements. To resolve the ambiguity, the composite literal must appear within parentheses.