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authorMuhammad Rifqi Fatchurrahman <muh_rif@live.com>2018-10-03 00:56:58 +0700
committerMuhammad Rifqi Fatchurrahman <muh_rif@live.com>2018-10-03 00:56:58 +0700
commit9438e56ae90755582be35b6756e5b97dd5d1334a (patch)
tree9834315a533f7a25dca61ae8216b678f43184068 /kotlin.html.markdown
parent67f785f10212ca827f25c83cfaa9dddc607a35c6 (diff)
[Kotlin/en] add kotlin operator overloading
Diffstat (limited to 'kotlin.html.markdown')
-rw-r--r--kotlin.html.markdown73
1 files changed, 70 insertions, 3 deletions
diff --git a/kotlin.html.markdown b/kotlin.html.markdown
index 86d1baa0..6ff7c1dc 100644
--- a/kotlin.html.markdown
+++ b/kotlin.html.markdown
@@ -65,7 +65,7 @@ fun helloWorld(val name : String) {
A template expression starts with a dollar sign ($).
*/
val fooTemplateString = "$fooString has ${fooString.length} characters"
- println(fooTemplateString) // => My String Is Here! has 18 characters
+ println(fooTemplateString) // => My String Is Here! has 18 characters
/*
For a variable to hold null it must be explicitly specified as nullable.
@@ -175,12 +175,12 @@ fun helloWorld(val name : String) {
// Objects can be destructured into multiple variables.
val (a, b, c) = fooCopy
println("$a $b $c") // => 1 100 4
-
+
// destructuring in "for" loop
for ((a, b, c) in listOf(fooData)) {
println("$a $b $c") // => 1 100 4
}
-
+
val mapData = mapOf("a" to 1, "b" to 2)
// Map.Entry is destructurable as well
for ((key, value) in mapData) {
@@ -347,6 +347,8 @@ fun helloWorld(val name : String) {
println(EnumExample.A) // => A
println(ObjectExample.hello()) // => hello
+
+ testOperator()
}
// Enum classes are similar to Java enum types.
@@ -376,6 +378,71 @@ 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)
+
+// instance += valueToAdd
+operator fun SomeClass.plusAssign(valueToAdd: Int) {
+ this.savedValue += valueToAdd
+}
+
+// -instance
+operator fun SomeClass.unaryMinus() = SomeClass(-this.savedValue)
+
+// ++instance or instance++
+operator fun SomeClass.inc() = SomeClass(this.savedValue + 1)
+
+// instance * other
+operator fun SomeClass.times(other: SomeClass) =
+ SomeClass(this.savedValue * other.savedValue)
+
+// an overload for multiply
+operator fun SomeClass.times(value: Int) = SomeClass(this.savedValue * value)
+
+// other in instance
+operator fun SomeClass.contains(other: SomeClass) =
+ other.savedValue == this.savedValue
+
+// instance[dummyIndex] = valueToSet
+operator fun SomeClass.set(dummyIndex: Int, valueToSet: Int) {
+ this.savedValue = valueToSet + dummyIndex
+}
+
+// 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
+}
```
### Further Reading