Types and Structs

Composite types and struct definitions. Results appear in the same fence: same-line // comments when short, multiline // blocks below the sample when not.

Struct Literal

Named fields preferred.

type User struct{ ID int; Name string }
u := User{ID: 1, Name: "Ada"}
u.ID  // 1

Slice Append

Grow slices with append.

s := []int{1, 2}
s = append(s, 3)
s  // [1 2 3]

Map Lookup

Comma-ok idiom for presence.

m := map[string]int{"a": 1}
v, ok := m["a"]
v  // 1
// ok == true

Array Fixed

Arrays have fixed length in the type.

var a [3]int
a[0] = 7
a[0]  // 7
// len(a) == 3

type Alias

Alias vs defined type.

type ID = int  // alias
type UserID int // distinct
UserID(3)  // 3

Slice Slicing

Slicing shares underlying array.

s := []int{0, 1, 2, 3}
s[1:3]  // [1 2]

make Map

Pre-size maps when known.

m := make(map[string]int, 8)
m["x"] = 1
len(m)  // 1

delete Map

Remove a key.

m := map[string]int{"a": 1}
delete(m, "a")
len(m)  // 0

Embedded Field

Promotion of embedded fields/methods.

type Point struct{ X, Y int }
type Dot struct{ Point }
d := Dot{Point: Point{1, 2}}
d.X  // 1

Struct Tags

Tags for encoding/json etc.

type T struct {
    Name string `json:"name"`
}
// reflect.TypeOf(T{}).Field(0).Tag.Get("json") == "name"

copy Slice

copy returns number of elements copied.

dst := make([]int, 2)
n := copy(dst, []int{1, 2, 3})
n  // 2
// dst == [1 2]

nil Slice vs Empty

nil and empty both len 0; nil is nil.

var s []int
s == nil  // true
len(s)    // 0

Comparable Keys

Map keys must be comparable.

m := map[[2]int]string{{1, 2}: "a"}
m[[2]int{1, 2}]  // "a"

Byte Slice String

Convert between string and []byte.

b := []byte("hi")
string(b)  // "hi"

Field Access Ptr

Go auto-dereferences struct pointers.

u := &User{ID: 9}
u.ID  // 9

Related

• Syntax and Basics - declarations
• Functions and Methods - methods on types
• Interfaces and Generics - interface satisfaction

External Related Links

• Go Language Specification - The formal language reference.
• Effective Go - Official guide to writing clear, idiomatic Go.
• Go by Example - Annotated practical code examples.
• The Go Programming Language (ebook) - Donovan & Kernighan.
• Learning Go (2nd Edition) - Jon Bodner.

Stack versions: Go 1.26.x · chi/gin/echo latest (verify at build)