🧊 Go Zero Value – Understand Default Values of Variables in Go

🧲 Introduction – What Is a Zero Value in Go?

In Go, when you declare a variable without explicitly initializing it, the variable is automatically assigned a zero value. This concept ensures safety and predictability, avoiding undefined or garbage data — a common issue in low-level languages like C or C++.

🎯 In this section, you’ll learn:

• What zero values are and why they exist
• Zero values of different Go data types
• How to check and use zero values in real programs
• Practical examples and best practices

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🧬 What Is the Zero Value?

A zero value is the default value given to a variable when it is declared but not explicitly initialized.

Example:

var x int
fmt.Println(x)  // Output: 0

Even though x isn’t initialized, Go ensures it holds a known, safe value (0 for int).

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📋 Zero Values by Data Type

Data Type	Zero Value	Example Output
int, int32	0	0
float64	0.0	0
bool	false	false
string	"" (empty)	""
pointer	nil	<nil>
interface{}	nil	<nil>
slice	nil	<nil>
map	nil	<nil>
channel	nil	<nil>
function	nil	<nil>
struct	All fields zeroed	Depends on field types

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🧪 Example – Zero Values in Action

package main

import "fmt"

type User struct {
    Name string
    Age  int
    Paid bool
}

func main() {
    var u User
    fmt.Println(u)           // Output: { 0 false}
    fmt.Println(u.Name)      // ""
    fmt.Println(u.Age)       // 0
    fmt.Println(u.Paid)      // false

    var ptr *int
    fmt.Println(ptr)         // <nil>

    var prices []float64
    fmt.Println(prices)      // []

    var done bool
    fmt.Println(done)        // false
}

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🧠 Why Zero Values Matter

✅ Safe Defaults – You don’t need to initialize every variable just to avoid compiler errors.

✅ Clear Semantics – Every type has a predictable zero value.

✅ Idiomatic Go – Many Go developers rely on zero values as the initial state of structs and variables.

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🧩 Common Use Cases

Struct Initialization Without Values

type Config struct {
    Port    int
    Enabled bool
}
var cfg Config
// cfg.Port == 0, cfg.Enabled == false

Slice and Map Defaults

var names []string  // names == nil
var scores map[string]int  // scores == nil

You must initialize slices/maps before using them:

names = append(names, "Alice")      // ✅
scores = make(map[string]int)       // ✅

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📌 Summary – Recap & Next Steps

Zero values make Go safe and predictable. Whether you’re declaring variables, defining structs, or handling collections, you can trust Go to set an appropriate starting value.

🔍 Key Takeaways:

• Every Go variable has a zero value if uninitialized
• 0, false, "", and nil are common zero values
• Use zero values when building structs or checking states
• Always initialize slices, maps, and channels before use

⚙️ Next: Learn how to import packages, including standard and third-party libraries, using Go’s import keyword.

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❓ FAQs – Go Zero Values

❓ What is the default value of an uninitialized variable in Go?
✅ The variable takes a zero value, depending on its type. For instance, int is 0, string is "", bool is false.

❓ Are slices and maps automatically initialized in Go?
✅ No. They default to nil and must be initialized using make() before use.

❓ Can zero values be used as default struct states?
✅ Yes. Structs automatically assign zero values to each field when declared.

❓ Is nil the zero value for all reference types?
✅ Yes. Pointers, maps, slices, functions, channels, and interfaces default to nil.

❓ Is the zero value always falsey in Go?
✅ Not always. Go doesn’t have truthy/falsy rules like JavaScript. Only booleans can be directly tested in if conditions.

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