Correct way to initialize empty slice

Question

To declare an empty slice  with a non-fixed size  is it better to do   mySlice1    make   int  0    or   mySlice2      int     Just wondering which one is the correct way

User · Answer

Empty slice and nil slice are initialized differently in Go:

var nilSlice []int 
emptySlice1 := make([]int, 0)
emptySlice2 := []int{}

fmt.Println(nilSlice == nil)    // true
fmt.Println(emptySlice1 == nil) // false
fmt.Println(emptySlice2 == nil) // false

As for all three slices, len and cap are 0.

User · Answer

As an addition to  ANisus  answer     below is some information from the  Go in action  book  which I think is worth mentioning   Difference between nil  amp  empty slices  If we think of a slice like this    pointer   length   capacity    then   nil slice     nil  0  0  empty slice   addr  0  0     points to an address      nil slice      They   re useful when you want to represent a slice that doesn   t exist  such as when an exception occurs in a function that returns a slice      Create a nil slice of integers  var slice   int       empty slice      Empty slices are useful when you want to represent an empty collection  such as when a database query returns zero results      Use make to create an empty slice of integers  slice    make   int  0      Use a slice literal to create an empty slice of integers  slice      int         Regardless of whether you   re using a nil slice or an empty slice  the built-in functions append  len  and cap work the same      Go playground example   package main  import        fmt     func main          var nil slice   int     var empty slice     int        fmt Println nil slice    nil  len nil slice   cap nil slice       fmt Println empty slice    nil  len empty slice   cap empty slice        prints   true 0 0 false 0 0

User · Answer

They are equivalent  See this code   mySlice1    make   int  0  mySlice2      int   fmt Println  mySlice1   cap mySlice1   fmt Println  mySlice2   cap mySlice2     Output   mySlice1 0 mySlice2 0   Both slices have 0 capacity which implies both slices have 0 length  cannot be greater than the capacity  which implies both slices have no elements  This means the 2 slices are identical in every aspect   See similar questions   What is the point of having nil slice and empty slice in golang   nil slices vs non-nil slices vs empty slices in Go language

User · Answer

The two alternative you gave are semantically identical  but using make   int  0  will result in an internal call to runtime makeslice  Go 1 14    You also have the option to leave it with a nil value   var myslice   int   As written in the Golang org blog      a nil slice is functionally equivalent to a zero-length slice  even though it points to nothing  It has length zero and can be appended to  with allocation    A nil slice will however json Marshal   into  null  whereas an empty slice will marshal into       as pointed out by   farwayer   None of the above options will cause any allocation  as pointed out by  ArmanOrdookhani

[arrays] Correct way to initialize empty slice

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