Pointers
example
func main() {
var a int = 45
var b *int = &a
fmt.Println(a, *b)
}
45 45
Use pointers to manipulate elements in array
func main() {
a := [3]int{1, 2, 3}
b := &a[0]
c := &a[1]
fmt.Printf("%v %p %p", a, b, c)
}
[1 2 3] 0xc000018180 0xc000018188
In go, you cannot access the memory by mathematical operations.
func main() {
a := [3]int{1, 2, 3}
b := &a[0]
c := &a[1] - 8
fmt.Printf("%v %p %p", a, b, c)
}
invalid operation: &a[1] - 8 (mismatched types *int and untyped int)
It is also possible to create pointers to objects
func main() {
var ms *myStruct = &myStruct{foo: 43}
fmt.Println(ms)
}
type myStruct struct {
foo int
}
&{43}
new() cannot specify a given value at creation time.
func main() {
var ms *myStruct = new(myStruct)
fmt.Println(ms)
}
type myStruct struct {
foo int
}
&{0}
The pointer's initial value is nil, so remember to check first avoiding runtime error.
func main() {
var ms *int
fmt.Println(ms)
}
<nil>
The method to get the value from the pointer object, line 4 is a syntax sugar.
func main() {
var ms *myStruct = &myStruct{foo: 32}
fmt.Println((*ms).foo)
fmt.Println(ms.foo)
}
32
32
array vs slice
Because array is a fixed length, it stores data directly.
But the slice is the underlying projection of the array, which stores a pointer to the first element of the underlying array
So when copying, array is deep copy, but slice is shallow copy
Map
Like Slice, a map stores a pointer to the first element of the underlying array.
