When passing slice to a function in Go, a copy of slice is passed instead of a pointer. 1. Modification of slice elements within the function will affect the original data because they share the same underlying array; 2. If the slice is reassigned within the function (such as using make or append), the external slice will not change; 3. To modify the slice itself, the pointer to the slice should be passed; 4. Use... to expand the slice into mutable parameters and pass it into the function to improve flexibility. Understanding the reference and value behavior of slices helps avoid common mistakes.
In Go, passing a slice to a function is a common operation. It does not require copying the entire structure like an array. The slice itself is a lightweight descriptor, which is efficient to pass. But if you don't understand the working mechanism behind it, you may get stuck in the pit when using it.
Slice is a reference type, and the copy is passed
When you pass a slice into a function, the function receives a copy of the slice, rather than a pointer to the original slice. That is, modifications to slice elements inside the function will affect the original data (because they all point to the same underlying array), but if you reassign slices in the function (such as using make or = assignment), the external slice will not change.
For example:
func modify(s []int) {
s[0] = 99
s = append(s, 4)
}
func main() {
a := []int{1, 2, 3}
modify(a)
fmt.Println(a) // Output [99 2 3]
} As you can see, the first element has changed, indicating that the underlying data is shared; but the newly added 4 does not appear in the original slice, because append may cause expansion, and a new underlying array is generated.
If you want to change the slice itself, you can pass the pointer
If you want the function to modify the length and capacity of the slice or make it point to another array, you need to pass the pointer of the slice.
func reset(s *[]int) {
*s = []int{4, 5, 6}
}
func main() {
a := []int{1, 2, 3}
reset(&a)
fmt.Println(a) // Output [4 5 6]
}The advantage of doing this is that you can control the changes in slices, but you should also be careful not to misoperate the pointer content.
Passing slices with variable parameters is more flexible
Sometimes you want the function to accept multiple elements instead of necessarily the entire slice, and you can implement mutable parameters with ... Of course, you can also do the opposite and spread the slice in ...
func print(nums ...int) {
fmt.Println(nums)
}
func main() {
data := []int{10, 20, 30}
print(data...) // Expand slice as parameters and pass in}This method is particularly useful when writing functions with strong versatility, such as logs, formatted output and other scenarios.
Basically that's it. slice is very commonly used in Go. Understanding whether it is a "reference" or a "value", and how to deal with capacity expansion and pointers can avoid many strange problems. When using it, pay a little attention to the change logic inside and outside the function, and you will basically not make any mistakes.
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