Kotlin - Anonymous Function and function type
Anonymous function
package examples
fun main() {
var f = {
println("hello")
}() // print hello
}
Function type
package examples
fun main() {
{
println("construstor ")
}()
var f = {
println("hello f1")
}
val f2: () -> Unit = {
println("hello f2")
}
f()
f2()
}
Implicit Return
- Anonymous function support return last line of value
package examples
fun main() {
var f = { //
"implicit return"
"ABC" // Print ABC
}
println(f())
}
Anonymous Function argument
package examples
fun main() {
// arg types return type arg names
val f : (String, String, String) -> Int = {a, b, c ->
a.length + b.length + c.length
}
println(f("aa", "fff", "ee"))
}
Default argument name: it
- "it" is the default argument name when there is only one parameter in anonymous function
package examples
fun main() {
val f : (String) -> Int = {
it.length
}
println(f("Gss"))
}
Return type inference
- No need to specify return type
package examples
fun main() {
val f = {
"hello"
}
println(f())
}
- Need provide arg name when no return type specified
package examples
fun main() {
val f = { name:String ->
"hello $name"
}
println(f("FF"))
}
Function as argument
package examples
fun main() {
println(count("hello", {it == 'l'}))
}
fun count(s:String, exclude:(Char) -> Boolean): Int {
var result = 0
for (c in s) if (!exclude(c)) result++
return result
}
- Lambda argument should be moved out of parentheses (Intellij suggestion)(When function is the latest argument)
package examples
fun main() {
println(count("hello") {it == 'l'})
}
fun count(s:String, exclude:(Char) -> Boolean): Int {
var result = 0
for (c in s) if (!exclude(c)) result++
return result
}
Function Inlining
- Inlining removes the need for the JVM to use an object instance and to perform variable memory allocations for the lambda.
package examples
fun main() {
println(count("hello") {it == 'l'})
}
inline fun count(s:String, exclude:(Char) -> Boolean): Int {
var result = 0
for (c in s) if (!exclude(c)) result++
return result
}
Function Reference
- Use "::" to reference a function
package examples
fun main() {
run(::printHello)
}
fun run(f: () -> Unit) {
f()
}
fun printHello() {
println("hello")
}
Return Function Type
package examples
fun main() {
create()("john")
}
fun create(): (String) -> Unit {
return {
println("hello $it")
}
}