Variable not declared, inside a if..else statement

Question

I'm just started learning go lang, and I am confused about declaring variables in go lang

for example I've declare req, er inside if...else statement.

if strings.EqualFold(r.Method, "GET") || strings.EqualFold(r.Method, "") {
    req, er := http.NewRequest(r.Method, r.Uri, b)
} else {
    req, er := http.NewRequest(r.Method, r.Uri, b)
}


if er != nil {
    // we couldn't parse the URL.
    return nil, &Error{Err: er}
}

// add headers to the request
req.Host = r.Host
req.Header.Add("User-Agent", r.UserAgent)
req.Header.Add("Content-Type", r.ContentType)
req.Header.Add("Accept", r.Accept)
if r.headers != nil {
    for _, header := range r.headers {
        req.Header.Add(header.name, header.value)
    }
}

But I've got error from terminal

./goreq.go:127: req declared and not used
./goreq.go:127: er declared and not used
./goreq.go:129: req declared and not used
./goreq.go:129: er declared and not used

seems like anything I declared inside If statement is not working... How can I solved it?

I don't know much about go, but it seems like if you declare req and er before the if statement and assign them inside the if statement, then the warnings (are they warnings or actually errors?) should go away. — jonhopkins
In Go, it is idiomatic to name the error result err rather than er — Ari Seyhun

Arjan Arjan · Accepted Answer · 2014-01-31T13:36:08

Because variables are only defined in the scope in which they are declared:

package main

import "fmt"

func main() {
    a := 1
    fmt.Println(a)
    {
        a := 2
        fmt.Println(a)
    }
    fmt.Println(a)
}

go play

The difference between = and := is that = is just assignment and := is syntax for variable declaration and assigment

This:

a := 1

is equivalent to:

var a int
a = 1

What you probably want is:

var req *http.Request
var er error
if strings.EqualFold(r.Method, "GET") || strings.EqualFold(r.Method, "") {
    req, er = http.NewRequest(r.Method, r.Uri, b)
} else {
    req, er = http.NewRequest(r.Method, r.Uri, b)
}


if er != nil {
    // we couldn't parse the URL.
    return nil, &Error{Err: er}
}

// add headers to the request
req.Host = r.Host
req.Header.Add("User-Agent", r.UserAgent)
req.Header.Add("Content-Type", r.ContentType)
req.Header.Add("Accept", r.Accept)
if r.headers != nil {
    for _, header := range r.headers {
        req.Header.Add(header.name, header.value)
    }
}

Variable not declared, inside a if..else statement

2 Answers