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🟡 Level 1 — Fundamentals
Foundation

Constants

Understand compile-time constants, untyped arbitrary precision, and the `iota` auto-incrementing enumerator.

Real-World Analogy (Mental Model)

“Constants are like blueprints carved into stone before the building is even constructed. They can never be altered once created.”

Architecture & Memory MapVisual Model
const (
    Sunday    = iota  // 0
    Monday    = iota  // 1
    Tuesday   = iota  // 2
    Wednesday = iota  // 3
)

Key Concepts & Rules To Remember

  • Declared with `const` keyword and evaluated strictly at compile time.
  • Untyped constants have infinite mathematical precision until assigned to a typed variable.
  • `iota` is an auto-incrementing integer index that simplifies enum definitions.
Step-by-Step Code

1. Declaring Constants & iota

`iota` resets to 0 whenever the `const` keyword appears and increments by 1 on each subsequent line in the block.

example.goGo 1.24+
package main

import "fmt"

const (
    StatusPending = iota // 0
    StatusActive         // 1 (iota continues)
    StatusClosed         // 2
)

const (
    _  = 1 << (10 * iota)
    KB // 1024
    MB // 1048576
    GB // 1073741824
)

func main() {
    fmt.Println(StatusActive) // 1
    fmt.Printf("1 GB = %d bytes\n", GB)
}

Common Beginner Pitfalls & Mistakes

Mistake: Trying to assign a runtime function return value to a constant (e.g. `const now = time.Now()`).
✅ Correct Way: Constants can ONLY be assigned values that are known at compile time.
Self Assessment

Knowledge Check

Verify your understanding with these interactive practice questions.

Quizzes

Quick checks for understanding

Multiple-choice with inline explanations—expand to see why.

When are Go constants evaluated?

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