Code Blocks

In Go, variable declarations can occur in various contexts, including outside of functions, as function parameters, and as local variables within functions. Each context where a declaration occurs is referred to as a block. Variables, constants, types, and functions declared outside of any functions are grouped in the package block. Additionally, import statements define names for other packages, and these names reside within the file block. Everything declared inside a function it's in the function block.

Shadowing Variables

Accessing an identifier defined in an outer block from within an inner block is possible in Go. When a declaration shares the same name as an identifier in an enclosing block, a shadowing variable is created, bearing the same name as the variable in the enclosing block. While the shadowing variable persists, access to the shadowed variable is restricted.

Using the := syntax can inadvertently result in variable shadowing. It's essential to exercise caution when using := to avoid unintentionally shadowing variables from an outer scope on the left-hand side unless deliberate shadowing is intended.

Creating a Showdowing Variable

run command

$ go run src/fundamentals/blocks.go
10
7
10
Redefining int type

package main

import "fmt"

func main() {
    originalVar := 10
    if originalVar > 5 {
        fmt.Println(originalVar)
        originalVar := 7
        fmt.Println(originalVar)
    }
    fmt.Println(originalVar)

    int := "Redefining int type"
    fmt.Println(int)
}

The Universe Block

A weird concept in Go is the universe block. Despite Go being a compact language with only 25 keywords, built-in types (e.g., int and string), constants (e.g., true and false), and functions (e.g., make or close) are not keywords. Similarly, nil is not classified as a keyword. Rather than designating them as keywords, Go treats these entities as predeclared identifiers and defines them within the universe block, encompassing all other blocks. Since these names are declared in the universe block, they can potentially be overshadowed in other scopes.

Redefinig Any Identifiers

Care must be taken to avoid redefining any identifiers in the universe block. Accidental redefinitions can lead to unexpected behavior.