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Kotlin の変数名またはスプレッド演算子の前の Kotlin 質問する

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Kotlin の変数名またはスプレッド演算子の前の Kotlin 質問する

Kotlinで変数名の前にアスタリスクを付けると、具体的に何をするのか知りたいです。この（*args）は、Spring Boot Kotlin の例:

@SpringBootApplication
open class Application {

    @Bean
    open fun init(repository: CustomerRepository) = CommandLineRunner {
        repository.save(Customer("Jack", "Bauer"))
        repository.save(Customer("Chloe", "O'Brian"))
        repository.save(Customer("Kim", "Bauer"))
        repository.save(Customer("David", "Palmer"))
        repository.save(Customer("Michelle", "Dessler"))
    }
}

fun main(args: Array<String>) {
    SpringApplication.run(Application::class.java, *args)
}

ベストアンサー1

オペレーター*はスプレッド演算子Kotlin で。

From the Kotlin Reference:

When you call a vararg-function, you can pass arguments individually, for example asList(1, 2, 3). if you already have an array and want to pass its contents to the function, use the spread operator (prefix the array with *):

It can be applied to an Array before passing it into a function that accepts vararg.

For Example...

If you have a function that accepts a varied number of arguments...

fun sumOfNumbers(vararg numbers: Int): Int {
    return numbers.sum()
}

Use the spread operator to pass an array's elements as the arguments:

val numbers = intArrayOf(2, 3, 4)
val sum = sumOfNumbers(*numbers)
println(sum) // Prints '9'

Notes:

  • The * operator is also the multiplication operator (of course).
  • The operator can only be used when passing arguments to a function. The result of the operation cannot be stored since it yields no value (it is purely syntactic sugar).
  • The operator may confuse some C/C++ programmers at first because it looks like a pointer is being de-referenced. It isn't; Kotlin has no notion of pointers.
  • The operator can be used in-between other arguments when calling a vararg-function. This is demonstrated in the example here.
  • The operator is similar to the apply function in various functional programming languages.

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