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Kotlin

Kotlin

is !is

- is !is:

if (obj is String) {
    print(obj.length)
}

if (obj !is String) { //     !(obj is String)
    print("Not a String")
}
else {
    print(obj.length)
}

, Kotlin , is- , .

fun demo(x: Any) {
    if (x is String) {
        print(x.length) // x    String
    }
}

, , (!is) :

    if (x !is String) return
    print(x.length) // x    String

, && ||:

    // x    String   `||`
    if (x !is String || x.length == 0) return

    // x is    String   `&&`
    if (x is String && x.length > 0) {
        print(x.length) // x    String
    }

when- while:

when (x) {
    is Int -> print(x + 1)
    is String -> print(x.length + 1)
    is IntArray -> print(x.sum())
}

, , . , :

""

, . , . Kotlin as:

val x: String = y as String

, null String, String nullable, .. y - null, . Java, nullable :

val x: String? = y as String?

"" (nullable)

, as?, null :

val x: String? = y as? String

, , as? non-null String, nullable.

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Kotlin

rangeTo .., in !in. (comparable) , . .

if (i in 1..10) { // equivalent of 1 <= i && i <= 10
    println(i)
}

(IntRange, LongRange, CharRange) : . for Java.

for (i in 1..4) print(i) // prints "1234"

for (i in 4..1) print(i) // prints nothing

, ? . downTo(), .

for (i in 4 downTo 1) print(i) // prints "4321"

, ? . step():

for (i in 1..4 step 2) print(i) // prints "13"

for (i in 4 downTo 1 step 2) print(i) // prints "42"

, , until:

for (i in 1 until 10) { // i in [1, 10), 10 is excluded
     println(i)
}

ClosedRange<T>.

, ClosedRange<T> , . : start endInclusive. contain. in/!in.

(IntProgression, LongProgression, CharProgression) . first, last increment. first , , increment. , last .

Iterable<N>, N - Int, Long Char. , for map, filter .. Progression for Java/JavaScript

for (int i = first; i != last; i += increment) {
  // ...
}

, .. , ClosedRange<T> *Progression*. , IntRange IntProgression ClosedRange<Int>. , IntProgression, IntRange. downTo() step() *Progression*(.: ).

fromClosedRange (companion object):

    IntProgression.fromClosedRange(start, end, increment)

last. , end. , - .

(.: Utility functions)

rangeTo()

rangeTo() *Range*:

class Int {
    //...
    operator fun rangeTo(other: Long): LongRange = LongRange(this, other)
    //...
    operator fun rangeTo(other: Int): IntRange = IntRange(this, other)
    //...
}

(Double, Float) rangeTo. Comparable :

    public operator fun <T: Comparable<T>> T.rangeTo(that: T): ClosedRange<T>

, , .

downTo()

- downTo() , :

fun Long.downTo(other: Int): LongProgression {
    return LongProgression.fromClosedRange(this, other, -1.0)
}

fun Byte.downTo(other: Int): IntProgression {
    return IntProgression.fromClosedRange(this, other, -1)
}

reversed()

reversed() *Progression* , .

fun IntProgression.reversed(): IntProgression {
    return IntProgression.fromClosedRange(last, first, -increment)
}

step()

- step() *Progression*, step ( ). , .

fun IntProgression.step(step: Int): IntProgression {
    if (step <= 0) throw IllegalArgumentException("Step must be positive, was: $step") //   
    return IntProgression.fromClosedRange(first, last, if (increment > 0) step else -step)
}

fun CharProgression.step(step: Int): CharProgression {
    if (step <= 0) throw IllegalArgumentException("Step must be positive, was: $step")
    return CharProgression.fromClosedRange(first, last, step)
}

, last last , (last - first) % increment == 0. :

    (1..12 step 2).last == 11  //     [1, 3, 5, 7, 9, 11]
    (1..12 step 3).last == 10  //     [1, 4, 7, 10]
    (1..12 step 4).last == 9   //     [1, 5, 9]
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, , , Software engineering - , . (. - " ")




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