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-rw-r--r--kotlin.html.markdown113
1 files changed, 51 insertions, 62 deletions
diff --git a/kotlin.html.markdown b/kotlin.html.markdown
index 6a6c1b66..9336d217 100644
--- a/kotlin.html.markdown
+++ b/kotlin.html.markdown
@@ -346,11 +346,6 @@ fun helloWorld(val name : String) {
return this.filter {it != c}
}
println("Hello, world!".remove('l')) // => Heo, word!
-
- println(EnumExample.A) // => A
- println(ObjectExample.hello()) // => hello
-
- testOperator()
}
// Enum classes are similar to Java enum types.
@@ -358,6 +353,8 @@ enum class EnumExample {
A, B, C
}
+fun printEnum() = println(EnumExample.A) // => A
+
/*
The "object" keyword can be used to create singleton objects.
We cannot instantiate it but we can refer to its unique instance by its name.
@@ -367,11 +364,18 @@ object ObjectExample {
fun hello(): String {
return "hello"
}
+
+ override fun toString(): String {
+ return "Hello, it's me, ${ObjectExample::class.simpleName}"
+ }
}
-fun useObject() {
- ObjectExample.hello()
- val someRef: Any = ObjectExample // we use objects name just as is
+
+fun useSingletonObject() {
+ println(ObjectExample.hello()) // => hello
+ // In Kotlin, "Any" is the root of the class hierarchy, just like "Object" is in Java
+ val someRef: Any = ObjectExample
+ println(someRef) // => Hello, it's me, ObjectExample
}
@@ -381,69 +385,54 @@ throws an exception if the value is null.
var b: String? = "abc"
val l = b!!.length
-/* You can add many custom operations using symbol like +, to particular instance
-by overloading the built-in kotlin operator, using "operator" keyword
-
-below is the sample class to add some operator, and the most basic example
-*/
-data class SomeClass(var savedValue: Int = 0)
+data class Counter(var value: Int) {
+ // overload Counter += Int
+ operator fun plusAssign(increment: Int) {
+ this.value += increment
+ }
-// instance += valueToAdd
-operator fun SomeClass.plusAssign(valueToAdd: Int) {
- this.savedValue += valueToAdd
-}
+ // overload Counter++ and ++Counter
+ operator fun inc() = Counter(value + 1)
-// -instance
-operator fun SomeClass.unaryMinus() = SomeClass(-this.savedValue)
+ // overload Counter + Counter
+ operator fun plus(other: Counter) = Counter(this.value + other.value)
-// ++instance or instance++
-operator fun SomeClass.inc() = SomeClass(this.savedValue + 1)
+ // overload Counter * Counter
+ operator fun times(other: Counter) = Counter(this.value * other.value)
-// instance * other
-operator fun SomeClass.times(other: SomeClass) =
- SomeClass(this.savedValue * other.savedValue)
+ // overload Counter * Int
+ operator fun times(value: Int) = Counter(this.value * value)
-// an overload for multiply
-operator fun SomeClass.times(value: Int) = SomeClass(this.savedValue * value)
+ // overload Counter in Counter
+ operator fun contains(other: Counter) = other.value == this.value
-// other in instance
-operator fun SomeClass.contains(other: SomeClass) =
- other.savedValue == this.savedValue
+ // overload Counter[Int] = Int
+ operator fun set(index: Int, value: Int) {
+ this.value = index + value
+ }
-// instance[dummyIndex] = valueToSet
-operator fun SomeClass.set(dummyIndex: Int, valueToSet: Int) {
- this.savedValue = valueToSet + dummyIndex
-}
+ // overload Counter instance invocation
+ operator fun invoke() = println("The value of the counter is $value")
-// instance()
-operator fun SomeClass.invoke() {
- println("instance invoked by invoker")
}
-
-/* return type must be Integer,
-so that, it can be translated to "returned value" compareTo 0
-
-for equality (==,!=) using operator will violates overloading equals function,
-since it is already defined in Any class
-*/
-operator fun SomeClass.compareTo(other: SomeClass) =
- this.savedValue - other.savedValue
-
-fun testOperator() {
- var x = SomeClass(4)
-
- println(x) // => "SomeClass(savedValue=4)"
- x += 10
- println(x) // => "SomeClass(savedValue=14)"
- println(-x) // => "SomeClass(savedValue=-14)"
- println(++x) // => "SomeClass(savedValue=15)"
- println(x * SomeClass(3)) // => "SomeClass(savedValue=45)"
- println(x * 2) // => "SomeClass(savedValue=30)"
- println(SomeClass(15) in x) // => true
- x[2] = 10
- println(x) // => "SomeClass(savedValue=12)"
- x() // => "instance invoked by invoker"
- println(x >= 15) // => false
+/* You can also overload operators through an extension methods */
+// overload -Counter
+operator fun Counter.unaryMinus() = Counter(-this.value)
+
+fun operatorOverloadingDemo() {
+ var counter1 = Counter(0)
+ var counter2 = Counter(5)
+ counter1 += 7
+ println(counter1) // => Counter(value=7)
+ println(counter1 + counter2) // => Counter(value=12)
+ println(counter1 * counter2) // => Counter(value=35)
+ println(counter2 * 2) // => Counter(value=10)
+ println(counter1 in Counter(5)) // => false
+ println(counter1 in Counter(7)) // => true
+ counter1[26] = 10
+ println(counter1) // => Counter(value=36)
+ counter1() // => The value of the counter is 36
+ println(-counter2) // => Counter(value=-5)
}
```