Declare slice or make slice?
In addition to fabriziom's answer, you can see more examples at "Go Slices: usage and internals", where a use for []int
is mentioned:
Since the zero value of a slice (
nil
) acts like a zero-length slice, you can declare a slice variable and then append to it in a loop:
// Filter returns a new slice holding only
// the elements of s that satisfy f()
func Filter(s []int, fn func(int) bool) []int {
var p []int // == nil
for _, v := range s {
if fn(v) {
p = append(p, v)
}
}
return p
}
It means that, to append to a slice, you don't have to allocate memory first: the nil
slice p int[]
is enough as a slice to add to.
Simple declaration
var s []int
does not allocate memory and s
points to nil
, while
s := make([]int, 0)
allocates memory and s
points to memory to a slice with 0 elements.
Usually, the first one is more idiomatic if you don't know the exact size of your use case.
Just found a difference. If you use
var list []MyObjects
and then you encode the output as JSON, you get null
.
list := make([]MyObjects, 0)
results in []
as expected.