Go doesn't have constructors so I'm wondering how you would properly initialize a struct inside a slice. I have trouble believing that the answer would be to initialize and copy all the structs twice?
package main
import "fmt"
// minQueueLen is smallest capacity that queue may have.
// Must be power of 2 for bitwise modulus: x % n == x & (n - 1).
const minQueueLen = 16
type Queue[T any] struct {
buf []T
}
func New[T any]() *Queue[T] {
return &Queue[T]{
buf: make([]T, minQueueLen),
}
}
type SomeStruct struct {
q Queue[int]
}
func main() {
someSlice := make([]SomeStruct, 10)
// Now buf is the wrong size because we didn't
// get to init it with the proper constructor.
// It would be very wasteful to initialize this
// struct twice (100s of thousands or more).
fmt.Println("Size of a buf: ", len(someSlice[0].q.buf))
}
Here is an example where the buffer of the queue must be a power of 2.
CodePudding user response:
You never really initialized it. Allocating a slice simply allocates the space, but does not initialize individual elements. Once you have the slice, you can loop through it and inialize:
func main() {
someSlice := make([]SomeStruct, 10)
for i:=range someSlice {
someSlice[i].q=*New[int]()
}
fmt.Println("Size of a buf: ", len(someSlice[0].q.buf))
}
You can also do:
func (s *SomeStruct) Init() {
s.q=Queue[int]{
buf: make([]int, minQueueLen),
}
}
func main() {
someSlice := make([]SomeStruct, 10)
for i:=range someSlice {
someSlice[i].Init()
}
fmt.Println("Size of a buf: ", len(someSlice[0].q.buf))
}