kotlin-return-break-continue
Kotlin return, break, continue Keywords
1. Overview
Simply put, Kotlin has three structural jump expressions: return, break, continue. In the next sections, we’ll cover their functionalities with and without a label.
2. Labels in Kotlin
We create a label by using an identifier followed by the “@” sign. For example, [email protected], [email protected] are valid labels.
To label an expression, we simply add the label in front of it:
[email protected] for (i in 1..10) {
// some code
}3. The Break Statement
Let’s have a look at an example:
@Test
fun givenLoop_whenBreak_thenComplete() {
var value = ""
for (i in "hello_world") {
if (i == '_') break
value += i.toString()
}
assertEquals("hello", value)
}Alternatively, we can use break with a label, which terminates the loop marked with that label:
@Test
fun givenLoop_whenBreakWithLabel_thenComplete() {
var value = ""
[email protected] for (i in 'a'..'d') {
for (j in 1..3) {
value += "" + i + j
if (i == 'b' && j == 1)
[email protected]_loop
}
}
assertEquals("a1a2a3b1", value)
}In this case, the outer loop is terminated when the i and j variables equal “b” and “1” respectively.
4. The Continue Statement
Without a label, continue will proceed to the next iteration of the enclosing loop:
@Test
fun givenLoop_whenContinue_thenComplete() {
var result = ""
for (i in "hello_world") {
if (i == '_') continue
result += i
}
assertEquals("helloworld", result)
}On the other hand, when we use continue with a label marking a loop, it will proceed to the next iteration of that loop:
@Test
fun givenLoop_whenContinueWithLabel_thenComplete() {
var result = ""
[email protected] for (i in 'a'..'c') {
for (j in 1..3) {
if (i == 'b') [email protected]_loop
result += "" + i + j
}
}
assertEquals("a1a2a3c1c2c3", result)
}In this example, we’ve used continue to skip one iteration of the loop labeled outer_loop.
5. The Return Statement
@Test
fun givenLambda_whenReturn_thenComplete() {
var result = returnInLambda();
assertEquals("hello", result)
}
private fun returnInLambda(): String {
var result = ""
"hello_world".forEach {
if (it == '_') return result
result += it.toString()
}
//this line won't be reached
return result;
}Return is also useful when we want to apply continue logic on anonymous functions:
@Test
fun givenAnonymousFunction_return_thenComplete() {
var result = ""
"hello_world".forEach(fun(element) {
if (element == '_') return
result += element.toString()
})
assertEquals("helloworld", result)
}In this example, the return statement will return to the caller of the anonymous fun, i.e. the forEach loop.
In the case of a lambda expression, we can also use return with a label to achieve a similar result:
@Test
fun givenLambda_whenReturnWithExplicitLabel_thenComplete() {
var result = ""
"hello_world".forEach [email protected]{
if (it == '_') {
[email protected]
}
result += it.toString()
}
assertEquals("helloworld", result)
}Alternatively, we can also return using an implicit label:
@Test
fun givenLambda_whenReturnWithImplicitLabel_thenComplete() {
var result = ""
"hello_world".forEach {
if (it == '_') {
// local return to the caller of the lambda, i.e. the forEach loop
[email protected]
}
result += it.toString()
}
assertEquals("helloworld", result)
}In the example above, the return statement will also return to the caller of the lambda – the forEach loop.
Finally, return can be used with a label to apply break logic to lambda expressions by returning to a label outside:
@Test
fun givenAnonymousFunction_returnToLabel_thenComplete() {
var result = ""
run [email protected]{
"hello_world".forEach {
if (it == '_') [email protected]
result += it.toString()
}
}
assertEquals("hello", result)
}6. Conclusion
The sample code could be found over on Github.
