Go make function
last modified April 11, 2024
In this artilc we describe the make function and shows how to use
it.
The make is a built-in function which allocates and initializes
an object of type slice, map, or chan.
func make(t Type, size ...IntegerType) Type
In case of a slice, the size specifies its length. A second integer may be
specified to set the capacity of the slice; it must not be smaller than the
length. The make([]int, 0, 5) allocates an underlying array of size
5 and returns a slice of length 0 and capacity 5 that is backed by this
underlying array.
In case of a map, an empty map is allocated with enough space to hold the specified number of elements. We can omit the size parameter, in which case a small starting size is allocated.
In case of a channel, the channel's buffer is initialized with the specified buffer capacity. If zero, or the size is omitted, the channel is unbuffered.
$ go version go version go1.22.2 linux/amd64
We use Go version 1.22.2.
Go make slice
In the first example, we create an empty slice of integers with
make.
package main
import (
"fmt"
)
func main() {
vals := make([]int, 5)
fmt.Println(vals)
vals[0] = 12
vals[1] = 18
vals[2] = 13
vals[3] = 19
vals[4] = 38
fmt.Println(vals)
vals2 := []int{12, 18, 13, 19, 38}
fmt.Println(vals2)
vals3 := []int{}
fmt.Println(vals3)
// vals3[0] = 12
// vals3[1] = 18
vals3 = append(vals3, 1)
vals3 = append(vals3, 2)
vals3 = append(vals3, 5)
vals3 = append(vals3, 6)
fmt.Println(vals3)
}
In the example, we create slice collections using make
funtion and literals.
vals := make([]int, 5) fmt.Println(vals)
We create a new slice with five elements initialized to 0.
vals[0] = 12 vals[1] = 18 vals[2] = 13 vals[3] = 19 vals[4] = 38 fmt.Println(vals)
Later, we fill the slice with some data.
vals2 := []int{12, 18, 13, 19, 38}
fmt.Println(vals2)
We can initialize the slice when we define it with literal notation.
vals3 := []int{}
fmt.Println(vals3)
Here we create an empty slice.
// vals3[0] = 12 // vals3[1] = 18
It is not possible to assign values to an empty slice.
vals3 = append(vals3, 1) vals3 = append(vals3, 2) vals3 = append(vals3, 5) vals3 = append(vals3, 6)
To add new values, the append function can be uzed.
$ go run main.go [0 0 0 0 0] [12 18 13 19 38] [12 18 13 19 38] [] [1 2 5 6]
Go make slice of slices
In the following example, we create a slice of slices with make.
package main
import "fmt"
func main() {
w := make([][]string, 3)
w1 := make([]string, 4)
w1[0] = "war"
w1[1] = "water"
w1[2] = "wrath"
w1[3] = "wrong"
w2 := make([]string, 3)
w2[0] = "car"
w2[1] = "cup"
w2[2] = "cloud"
w3 := make([]string, 2)
w3[0] = "boy"
w3[1] = "brown"
w[0] = w1
w[1] = w2
w[2] = w3
fmt.Println(w)
}
The example creates a slice of a string slices of various length.
w := make([][]string, 3)
We create a slice of slices.
w1 := make([]string, 4) w1[0] = "war" w1[1] = "water" w1[2] = "wrath" w1[3] = "wrong"
Each of the subslices is separately created with make and
initialized.
$ go run main.go [[war water wrath wrong] [car cup cloud] [boy brown]]
Go make map
In the next example, we create a new map with make.
package main
import "fmt"
func main() {
benelux := make(map[string]string)
benelux["be"] = "Belgium"
benelux["nl"] = "Netherlands"
benelux["lu"] = "Luxembourgh"
fmt.Println(benelux)
fmt.Printf("%q\n", benelux)
}
The example creates a new map and adds three pairs to it.
$ go run main.go map[be:Belgium lu:Luxembourgh nl:Netherlands] map["be":"Belgium" "lu":"Luxembourgh" "nl":"Netherlands"]
Go make channel
In the following example, we use the make function to create a
channel. A channel is an object through which goroutines communicate.
package main
import (
"fmt"
)
func fib(n int, c chan int) {
x, y := 0, 1
for i := 0; i < n; i++ {
c <- x
x, y = y, x+y
}
close(c)
}
func main() {
c := make(chan int, 10)
go fib(cap(c), c)
for i := range c {
fmt.Println(i)
}
}
A series of fibonacci values is generated inside the fib goroutine. The values are one by one send to the caller goroutine via a channel.
$ go run main.go 0 1 1 2 3 5 8 13 21 34
Source
The Go Programming Language Specification
In this article we have showed how to use the make built-in
function.
Author
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