Go Fundamentals Basics

10 examples to get you started with Go Fundamentals - 7 basic and 3 intermediate.

Prerequisites

Install Go 1.26.x or later from go.dev/dl.
Create a module: mkdir hello && cd hello && go mod init example.com/hello.
Run any snippet with go run . after saving it as main.go in that directory.

Basic Examples

1. Hello, main

The smallest executable: a main package with func main().

package main
 
import "fmt"
 
func main() {
    fmt.Println("hello, Go")
}

package main marks an executable, not a library.
import "fmt" brings in the formatted I/O package from the standard library.
go run . compiles and runs without leaving a binary in the directory.

Related: How Go Programs Are Structured - packages, linking, and the toolchain

2. Variables and short declaration

Declare with var or use := inside functions.

package main
 
import "fmt"
 
func main() {
    var name string = "Go"
    year := 2009
    fmt.Println(name, year)
}

:= infers type and can only appear inside functions.
var works at package level; := does not.
Unused variables are compile errors - Go enforces clean locals.

Related: Variables, Constants & Scope - declaration styles and scope rules

3. Zero values

Variables get a default without explicit initialization.

package main
 
import "fmt"
 
func main() {
    var count int
    var ready bool
    var label string
    fmt.Printf("int=%d bool=%t string=%q\n", count, ready, label)
}

Numeric types default to 0, bool to false, strings to "".
Pointers, slices, maps, channels, and interfaces default to nil.
Rely on zero values for "empty" sentinel states when that is idiomatic.

Related: Zero Values and Initialization - per-type defaults and init patterns

4. Constants and iota

const names compile-time values; iota builds enumerated constants.

package main
 
import "fmt"
 
const (
    Sunday = iota
    Monday
    Tuesday
)
 
func main() {
    fmt.Println(Sunday, Monday, Tuesday) // 0 1 2
}

iota resets to 0 in each const block and increments per line.
Constants must be expressible at compile time (no runtime calls).
Use typed constants when you need a distinct type, not just an untyped number.

Related: Variables, Constants & Scope - iota patterns and scope

5. Basic types and string iteration

Strings are UTF-8 byte sequences; iterate by rune with range.

package main
 
import "fmt"
 
func main() {
    s := "café"
    for i, r := range s {
        fmt.Printf("%d: %U\n", i, r)
    }
}

range over a string yields byte index and rune (int32), not byte offset for multi-byte chars.
len(s) counts bytes, not runes.
Use []rune(s) when you need random access by character index.

Related: Numeric Types, Strings, Runes & Byte Slices - UTF-8, runes, and conversions

6. Slices

Slices are dynamic views over an underlying array.

package main
 
import "fmt"
 
func main() {
    nums := []int{1, 2, 3}
    nums = append(nums, 4)
    fmt.Println(nums, len(nums), cap(nums))
}

append may allocate a new backing array when capacity is exceeded.
len is element count; cap is backing array size from the slice header.
A nil slice is valid and works with append and range.

Related: Arrays, Slices & Maps at a Glance - len/cap and sharing

7. Maps

Maps are hash tables keyed by comparable types.

package main
 
import "fmt"
 
func main() {
    ages := map[string]int{"ada": 36}
    ages["linus"] = 55
    if v, ok := ages["grace"]; ok {
        fmt.Println(v)
    } else {
        fmt.Println("grace: unknown")
    }
}

The two-value form v, ok := m[key] distinguishes missing keys from zero values.
Maps must be initialized with make or a literal before assignment.
Iteration order is randomized - do not depend on key order.

Related: Arrays, Slices & Maps at a Glance - map iteration and gotchas

Intermediate Examples

8. Structs and embedding

Group fields in a struct; embed to promote methods and fields.

package main
 
import "fmt"
 
type Person struct{ Name string }
type Employee struct {
    Person
    ID int
}
 
func main() {
    e := Employee{Person: Person{Name: "Grace"}, ID: 1}
    fmt.Println(e.Name, e.ID) // promoted field
}

Embedded fields promote to the outer type's namespace.
Embedding is composition, not classical inheritance.
Use explicit field names when promotion would be ambiguous.

Related: Structs, Embedding & Field Promotion - modeling and promotion rules

9. Pointers

& takes an address; * dereferences. Methods can use pointer receivers to mutate.

package main
 
import "fmt"
 
type Counter struct{ n int }
 
func (c *Counter) Inc() { c.n++ }
 
func main() {
    c := &Counter{}
    c.Inc()
    fmt.Println(c.n)
}

Go passes structs by value unless you pass a pointer.
Pointer receivers avoid copying large structs and allow mutation.
nil pointers panic on dereference - check before use.

Related: Pointers & the Address-of Operator - when pointers help vs hurt

10. Package layout sketch

Split main from reusable code across packages in one module.

// main.go
package main
 
import "example.com/hello/greet"
 
func main() {
    greet.Hello("world")
}

// greet/greet.go
package greet
 
import "fmt"
 
func Hello(name string) {
    fmt.Printf("hello, %s\n", name)
}

Only main packages build executables; greet is a library package.
Exported names start with uppercase (Hello); lowercase stays private.
Run from module root: go run . with both files in place.

Related: How Go Programs Are Structured - modules, imports, and internal/

A Tour of Go - Official interactive introduction to Go.
Go Tutorials (Official) - Official multi-part tutorials.
Go Playground - Official online editor and runner.
Get Programming with Go (Manning) - Nathan Youngman & Roger Peppé.
The Go Programming Language (ebook) - Donovan & Kernighan.

Stack versions: This page was written for Go 1.26.x (Green Tea GC default, go fix modernizers - verify patch at build), chi (latest - verify at build), gin (latest - verify at build), echo (latest - verify at build), google.golang.org/grpc (latest - verify at build), sigs.k8s.io/controller-runtime (latest - verify at build), kubebuilder (latest - verify at build), tinygo (latest - verify board targets at build), wazero (latest - verify at build), and golangci-lint (latest - verify linter set at build).

Prerequisites

Install Go 1.26.x or later from go.dev/dl.
Create a module: mkdir hello && cd hello && go mod init example.com/hello.
Run any snippet with go run . after saving it as main.go in that directory.

Basic Examples

1. Hello, main

The smallest executable: a main package with func main().

package main
 
import "fmt"
 
func main() {
    fmt.Println("hello, Go")
}

package main marks an executable, not a library.
import "fmt" brings in the formatted I/O package from the standard library.
go run . compiles and runs without leaving a binary in the directory.

Related: How Go Programs Are Structured - packages, linking, and the toolchain

2. Variables and short declaration

Declare with var or use := inside functions.

package main
 
import "fmt"
 
func main() {
    var name string = "Go"
    year := 2009
    fmt.Println(name, year)
}

:= infers type and can only appear inside functions.
var works at package level; := does not.
Unused variables are compile errors - Go enforces clean locals.

Related: Variables, Constants & Scope - declaration styles and scope rules

3. Zero values

Variables get a default without explicit initialization.

package main
 
import "fmt"
 
func main() {
    var count int
    var ready bool
    var label string
    fmt.Printf("int=%d bool=%t string=%q\n", count, ready, label)
}

Numeric types default to 0, bool to false, strings to "".
Pointers, slices, maps, channels, and interfaces default to nil.
Rely on zero values for "empty" sentinel states when that is idiomatic.

Related: Zero Values and Initialization - per-type defaults and init patterns

4. Constants and iota

const names compile-time values; iota builds enumerated constants.

package main
 
import "fmt"
 
const (
    Sunday = iota
    Monday
    Tuesday
)
 
func main() {
    fmt.Println(Sunday, Monday, Tuesday) // 0 1 2
}

iota resets to 0 in each const block and increments per line.
Constants must be expressible at compile time (no runtime calls).
Use typed constants when you need a distinct type, not just an untyped number.

Related: Variables, Constants & Scope - iota patterns and scope

5. Basic types and string iteration

Strings are UTF-8 byte sequences; iterate by rune with range.

package main
 
import "fmt"
 
func main() {
    s := "café"
    for i, r := range s {
        fmt.Printf("%d: %U\n", i, r)
    }
}

range over a string yields byte index and rune (int32), not byte offset for multi-byte chars.
len(s) counts bytes, not runes.
Use []rune(s) when you need random access by character index.

Related: Numeric Types, Strings, Runes & Byte Slices - UTF-8, runes, and conversions

6. Slices

Slices are dynamic views over an underlying array.

package main
 
import "fmt"
 
func main() {
    nums := []int{1, 2, 3}
    nums = append(nums, 4)
    fmt.Println(nums, len(nums), cap(nums))
}

append may allocate a new backing array when capacity is exceeded.
len is element count; cap is backing array size from the slice header.
A nil slice is valid and works with append and range.

Related: Arrays, Slices & Maps at a Glance - len/cap and sharing

7. Maps

Maps are hash tables keyed by comparable types.

package main
 
import "fmt"
 
func main() {
    ages := map[string]int{"ada": 36}
    ages["linus"] = 55
    if v, ok := ages["grace"]; ok {
        fmt.Println(v)
    } else {
        fmt.Println("grace: unknown")
    }
}

The two-value form v, ok := m[key] distinguishes missing keys from zero values.
Maps must be initialized with make or a literal before assignment.
Iteration order is randomized - do not depend on key order.

Related: Arrays, Slices & Maps at a Glance - map iteration and gotchas

Intermediate Examples

8. Structs and embedding

Group fields in a struct; embed to promote methods and fields.

package main
 
import "fmt"
 
type Person struct{ Name string }
type Employee struct {
    Person
    ID int
}
 
func main() {
    e := Employee{Person: Person{Name: "Grace"}, ID: 1}
    fmt.Println(e.Name, e.ID) // promoted field
}

Embedded fields promote to the outer type's namespace.
Embedding is composition, not classical inheritance.
Use explicit field names when promotion would be ambiguous.

Related: Structs, Embedding & Field Promotion - modeling and promotion rules

9. Pointers

& takes an address; * dereferences. Methods can use pointer receivers to mutate.

package main
 
import "fmt"
 
type Counter struct{ n int }
 
func (c *Counter) Inc() { c.n++ }
 
func main() {
    c := &Counter{}
    c.Inc()
    fmt.Println(c.n)
}

Go passes structs by value unless you pass a pointer.
Pointer receivers avoid copying large structs and allow mutation.
nil pointers panic on dereference - check before use.

Related: Pointers & the Address-of Operator - when pointers help vs hurt

10. Package layout sketch

Split main from reusable code across packages in one module.

// main.go
package main
 
import "example.com/hello/greet"
 
func main() {
    greet.Hello("world")
}

// greet/greet.go
package greet
 
import "fmt"
 
func Hello(name string) {
    fmt.Printf("hello, %s\n", name)
}

Only main packages build executables; greet is a library package.
Exported names start with uppercase (Hello); lowercase stays private.
Run from module root: go run . with both files in place.

Related: How Go Programs Are Structured - modules, imports, and internal/

A Tour of Go - Official interactive introduction to Go.
Go Tutorials (Official) - Official multi-part tutorials.
Go Playground - Official online editor and runner.
Get Programming with Go (Manning) - Nathan Youngman & Roger Peppé.
The Go Programming Language (ebook) - Donovan & Kernighan.

Stack versions: This page was written for Go 1.26.x (Green Tea GC default, go fix modernizers - verify patch at build), chi (latest - verify at build), gin (latest - verify at build), echo (latest - verify at build), google.golang.org/grpc (latest - verify at build), sigs.k8s.io/controller-runtime (latest - verify at build), kubebuilder (latest - verify at build), tinygo (latest - verify board targets at build), wazero (latest - verify at build), and golangci-lint (latest - verify linter set at build).

Go Fundamentals Basics

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Go Fundamentals Basics