Zero Values | Engineering Interview Kit

TL;DR

In Go, there is no such thing as an “uninitialized” variable. If you declare a variable but don’t assign it a value, Go automatically gives it a Zero Value corresponding to its type (e.g., 0 for numbers, "" for strings, nil for pointers/maps/slices).

Mental Model

How It Works

This feature ensures memory safety and predictability. In languages like C, an uninitialized variable contains “garbage” memory leftovers. In Go, it is immediately wiped clean and set to a safe default.

Common Zero Values:

Numeric types (int, float64): 0
Booleans (bool): false
Strings (string): "" (Empty string)
Pointers, functions, interfaces, slices, channels, and maps: nil

Example

package main

import "fmt"

func main() {
	var count int
	var isActive bool
	var name string
	var users []string // A slice

	fmt.Printf("count: %v\n", count)       // 0
	fmt.Printf("isActive: %v\n", isActive) // false
	fmt.Printf("name: %q\n", name)         // ""
	
	if users == nil {
		fmt.Println("users slice is nil")  // This prints!
	}
}

Common Interview Questions

Can you assign `nil` to a string in Go?

No. Unlike Java or C#, strings in Go are value types, not references. A string can never be nil. Its zero value is strictly an empty string "". If you need a nullable string (e.g., for JSON parsing where a field might be missing), you must use a string pointer *string.

What is the zero value of a Struct?

The zero value of a struct is the struct itself, with all of its fields recursively set to their respective zero values. For example, var u User results in {Name: "", Age: 0, IsAdmin: false}.