Why Can't I Declare a Variable Outside a Function in Go?

Non-Declaration Statement Outside Function Body in Go

In Go, a non-declaration statement outside a function body triggers an error. This is observed in the code snippet:

package apitest

import (
    "fmt"
)

test := "This is a test."

func main() {
    fmt.Println(test)
    test = "Another value"
    fmt.Println(test)
}

This code attempts to declare a variable outside the main() function and assign a value to it. However, Go does not allow non-declaration statements outside of function bodies.

Idiomatic Approach

The idiomatic Go way to declare a variable accessible from anywhere within a package but not necessarily a constant is:

var test = "This is a test"

• Using the var keyword declares a variable named test.
• The lowercase "t" indicates that the variable is only visible within the package (unexported).
• The assignment operator = initializes the variable with the value "This is a test".

Variable Characteristics

The test variable:

• Is accessible from anywhere within the apitest package.
• Can be reassigned, making it changeable.

Additional Notes

• Instead of var test = "This is a test", you could write var test string = "This is a test", but it is not considered idiomatic Go.
• Go also provides the init function for complex package initializations or setting up package state. Init is called before main runs.

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