為什麼在 Go 中會出現「函數體以外的非宣告語句」錯誤？

Non-Declaration Statement Outside Function Body in Go

In Go, declaring a variable outside of a function body typically leads to the "non-declaration statement outside function body" error. This occurs because Go strictly enforces scoping rules, requiring variables to be declared within the appropriate block (e.g., inside a function).

Idiomatic Global Variable Declaration

To create a globally accessible variable that is changeable but not a constant, the syntax is:

var test = "This is a test"

• The var keyword is used for variable declaration.
• The name of the variable (test in this case) should start with a lowercase letter to indicate its visibility within the package (unexported).
• The = sign assigns a value to the variable.

Example:

package apitest

import (
    "fmt"
)

var test = "This is a test" // Globally accessible variable

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

Extended Explanation

• Variable Initialization in Functions: Inside functions, you can declare a variable and assign it a value later using the := operator. However, := is not valid for global variable declarations.
• Type Inference: Go supports type inference, where the compiler can determine the type of a variable based on its initial value.
• Changing Package-Level Variables: Package-level variables, including globally accessible variables, can be changed from within functions using the same variable name (e.g., changeTest(newVal) in the provided code snippet).
• Init Function: For complex package initialization, Go provides the init function, which is automatically executed before main(). It can be used to set up initial states for the package.

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