Table of Contents
Arrays
When you use range with an array or a slice, it iterates over the indices and values of the elements.
package main
import "fmt"
func main() {
intArr := []int{11, 12, 13, 14}
for index, value := range intArr {
fmt.Printf("index=%d value(d)=%d value(v)=%#v\n", index, value, value)
}
}
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Output:
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index=0 value(d)=11 value(v)=11
index=1 value(d)=12 value(v)=12
index=2 value(d)=13 value(v)=13
index=3 value(d)=14 value(v)=14Strings
When iterating over a string with range, it returns the index and the Unicode code point (rune – int32) of each character.
package main
import "fmt"
func main() {
inputString := "ROBpike"
// here value is Rune of int32
for index, value := range inputString {
fmt.Printf("index=%d type(T)=%T value(v)=%#v Rune(c)=%c\n", index, value, value, value)
}
}
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Output:
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index=0 type(T)=int32 value(v)=82 Rune(c)=R
index=1 type(T)=int32 value(v)=79 Rune(c)=O
index=2 type(T)=int32 value(v)=66 Rune(c)=B
index=3 type(T)=int32 value(v)=112 Rune(c)=p
index=4 type(T)=int32 value(v)=105 Rune(c)=i
index=5 type(T)=int32 value(v)=107 Rune(c)=k
index=6 type(T)=int32 value(v)=101 Rune(c)=eMap
When you use range with a map, it iterates over the key-value pairs.
package main
import "fmt"
func main() {
// Key: String, Value : int
m := map[string]int{"a": 1, "b": 2, "c": 3}
for k, v := range m {
fmt.Printf("Key: %s, Value: %d\n", k, v)
}
// Key: int, Value : String
n := map[int]string{5: "d", 6: "e", 7: "f"}
for k, v := range n {
fmt.Printf("Key: %d, Value: %s\n", k, v)
}}
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Output:
---------------------------------------------
// Key: String, Value : int
Key: a, Value: 1
Key: b, Value: 2
Key: c, Value: 3
// Key: int, Value : String
Key: 5, Value: d
Key: 6, Value: e
Key: 7, Value: f
Channels
When iterating over a channel with range, it retrieves values sent through the channel until the channel is closed.
package main
import "fmt"
func main() {
ch := make(chan int, 3)
ch <- 1
ch <- 2
ch <- 3
close(ch)
for v := range ch {
fmt.Println(v)
}
}
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Output:
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1
2
3
Notes
If you only need the index or key, you can ignore the value using the blank identifier _:
for i := range arr {
fmt.Println(i)
}If you only need the value, you can ignore the index/key similarly:
for _, v := range arr {
fmt.Println(v)
}The range keyword makes iterating over various data structures straightforward and readable in Go.