[Go] Ch1: Go Basics - 03 Go Data Structure: `Structs`

Structs (Structures)

A struct or structure is a collection of fields.

1. Defining a struct

Using struct keyword to create a new structure type.

type StructName struct {
    field1 fieldType1
    field2 fieldType2
    ...
}

Example:

type Vertex struct {
    X int
    Y int
}

2. Accessing Struct Fields (Members)

Struct fields are accessed using a dot.

v := Vertrx{1, 2}
v.X = 4
fmt.Println(v.X) // 4

Pointers to Structs

1. Pointer

A pointer holds the memory address of a value.

The type *T is a pointer to a T value. Its zero value is nil.

var *p int

The & operator generates a pointer to its operand.

i := 42
p = &i

The * operator denotes the pointer’s underlying value.

fmt.Println(*p) // read i through the pointer p
*p = 21         // set i through the pointer p

This is known as "dereferencing" or "indirecting".

• Unlike C, Go has no pointer arithmetic (沒有指針運算).

2. Pointers to Structs

Struct fields can be accessed through a struct pointer.

The syntax to create a pointer to a struct is as follows.

s := StructType{...}
p := &s

// or
p := &StructType{...}

Example:

v := Vertex{1, 2}
p := &v

q := &Vertex{3, 4}

3. Accessing the field of Struct Pointer

To access the field X of a struct when we have the struct pointer p, we need to use dereferencing syntax (*p) to get the actual value of struct it is pointing to and use (*p).X to access X of that struct value.

However, that notation is cumbersome, so the language permits us instead to write just p.X, without the explicit dereference.

v := Vertex{1, 2}
p := &v
p.X = 1e3
fmt.Println(v) // {1000, 2}