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...el

Answer 1

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)
    }
}

Answer 2

This is because you have declared the variables req and er inside the if else condition and are trying to use it outside the scope (the scope is just the if and else inside which they are declared).

You need to declare er and req outside the if else