golang if初始化语句的作用域为内部if块。 为什么？ [重复]

Question

This question already has an answer here:

• Golang mixed assignation and declaration 3 answers

I've found a bug in my code

func receive() (err error) {
    if v, err := produce(); err == nil {
        fmt.Println("value: ", v)
    }
    return
}

Error is never returning from this function, but I was absolutely sure it should.

After some testing I understood that err is redeclared in the if statement. More than that - all variables are always redeclared in short variable assignment inside if statement, despite they were declared before.

This is working code

func receive() (err error) {
    v, err := produce()
    if err == nil {
        fmt.Println("value: ", v)
    }
    return
}

Here is an example: https://play.golang.org/p/1AWBsPbLiI1

Seems like if statement

//some code
if <init_statement>; <expression> {}
//more code

is equivalent to

//some code
{
    <init_statement>
    if expression {}
}
//more code

So, my questions:

1) why existing variables are not used

2) why such scoping is not mentioned in documentation/language spec

3) why compiler doesn't say that no one returns a value

</div>

Answer 1

1) Because the language spec says so.

2) It is:

Each "if", "for", and "switch" statement is considered to be in its own implicit block"

3) You did return at the end of your function. Do not use named return values.