Lesson 02 of 20

6 mins read

Variables, Zero Values, Constants & iota

In Plain English

Go offers explicit variable declarations with var and type-inferred short declarations with := inside functions. Uninitialized variables automatically receive their zero value (0, "", false, nil). The iota enumerator simplifies successive integer constant definitions.

The Mental Model

"In Go, uninitialized variables are never filled with random memory garbage: declaring a variable is like receiving a freshly cleaned whiteboard erased to 0, empty string, or false."

Deep Dive: How It Works

Short Declaration (:=): Infers type automatically at compile time (only valid inside function bodies).

Guaranteed Zero Values: int/float = 0, string = "", bool = false, pointers/slices/maps = nil.

iota Constant Generator: Automatically increments by 1 for each line in a const () block.

Syntax Blueprint

var total int = 10
count := 42 // Inferred int
const (
    StatusPending = iota // 0
    StatusActive         // 1
)

Declare explicit vars, short inferred variables, and auto-incrementing constants with iota.

Core Rules to Remember

Zero Memory Safety: Variables are never left uninitialized, preventing catastrophic memory leak read bugs.

Strict Type System: No implicit type conversion: int32 and int64 cannot be added without explicit cast int64(x).

iota Constants: Provides clean, type-safe enumerated state constants without manual number assignment.

Common Beginner Traps & How to Fix Them

Mistake:Using short declaration := at package global scope outside of functions.

Why it happens: := is only valid inside function bodies.

How to fix: Use var name = value or var name Type at package level.

Pro Tip: Group related package constants inside a single const () block for readability and documentation.

Live Interactive Example

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Typed Constants and iota States

Go 1.22 / Runtime

Output Console

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How it works: StateRunning evaluates to 1 via iota, and requestCount is zero-initialized to 0.

Your Turn: Micro Challenge

No pressure! Edit the starter code below and test your solution with instant feedback.

Micro Exercise

Inspect StateStopped iota Code

Print "Stopped State: %d\n" using the StateStopped constant with fmt.Printf.

Sandbox Output

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