The do-while is a popular programming loop found in many languages such as C++, Java, or JavaScript. It is similar to the while loop but with the difference that the body of the do-while is executed at least once. In Go, there is no special expression to create the do-while loop, but we can easily simulate it using a for loop. We just need to ensure that it executes at least once.
The classic for has the form of:
for <initialization>; <condition>; <post-condition> {
<loopBody>
}
To ensure that it executes at least once, the <condition> must be true for the first iteration and be dependent on the loop stop condition in subsequent iterations:
for next := true; next; next=<condition> {
<loopBody>
}
There is also a simpler form of the do-while loop in Go, in which the <condition> of the for loop is checked after the <loopBody> and if it is not true the loop is exited:
for {
<loopBody>
if !<condition> {
break
}
}
Examples
The first version of the do-while loop:
Print the i variable if the value is less than 5:
i := 0
for next := true; next; next = i < 5 {
fmt.Println(i)
i++
}
Output:
0
1
2
3
4
Check that the loop is executed at least once:
i := 10
for next := true; next; next = i < 5 {
fmt.Println(i)
i++
}
Output:
10
The second version of the do-while loop:
Print the i variable if the value is less than 5:
i := 0
for {
fmt.Println(i)
i++
if i >= 5 {
break
}
}
Output:
0
1
2
3
4
This version of the loop is also executed at least once 😉:
i := 10
for {
fmt.Println(i)
i++
if i >= 5 {
break
}
}
Output:
10
