tulkdan.dev
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Kotlin/ControlFlow.org
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Kotlin/ControlFlow.org
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* Control Flow
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** Conditional expressions
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Kotlin provides =if= and =when= for checking conditional expressions
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*** When
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Use =when= when you have a conditional expressions with multiple branches.
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=when= can be used either as a statement or as an expression.
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Heres how to use:
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+ Place the conditional expression within parentheses =()= and the actions to take within curly braces ={}=
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+ Use =->= in each branch to separate each condition from each action
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#+begin_src kotlin
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val obj = "Hello"
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when (obj) {
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"1" -> println("One")
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"Hello" -> println("Greeting")
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else -> println("Unknown")
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}
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#+end_src
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#+RESULTS:
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: Greeting
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Here's an example of using =when= as an expression, the syntax is assigned immediately to a variable:
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#+begin_src kotlin
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val result = when (obj) {
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"1" -> "One"
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"Hello" -> "Greeting"
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else -> "Unknown"
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}
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println(result)
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#+end_src
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#+RESULTS:
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: Greeting
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If =when= is used as an expression, the else branch is mandatory, unless the compiler can detect
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that all possible cases are covered by the branch conditions.
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The previous example showed that =when= is useful for matching a variable.
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=when= is also useful when you need to check a chain of Boolean expressions
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#+begin_src kotlin
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val temp = 18
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val description = when {
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temp < 0 -> "very cold"
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temp < 10 -> "a bit cold"
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temp < 20 -> "warm"
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else -> "hot"
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}
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println(description)
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#+end_src
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#+RESULTS:
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: warm
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** Ranges
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The most commom way to create a range in Kotlin is to use the =..= operator.
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For example, =1..4= is equivalent to =1, 2, 3, 4=.
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To declare a range that doesn't include the end value, use the =..<= operator.
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For example, =1..<4= is equivalent to =1, 2, 3=.
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To declare a range in reverse order, use =downTo=.
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For example, =4 downTo 1= is equivalent to =4, 3, 2, 1=.
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To declare a range that increments in a step, use =step= and the desired increment value.
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For example, =1..5 step 2= is equivalent to =1, 3, 5=.
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You can also do the same with =Char= ranges:
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+ ='a'..'d'= = ='a', 'b', 'c', 'd'=
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+ ='z' downTo 's' step 2= = ='z', 'x', 'v', 't'=