CODEWITHSUNDEEP
javaoperatorskotlin
fikr4n
fikr4n

Reputation: 3420

Why getting class in Kotlin using double-colon (::)?

We know that double-colon (::) is used to get function (callable) reference in Kotlin, e.g. String::compareTo, "string"::compareTo.

In Java we use SomeClass.class and someInstance.getClass() to get the class. Why in Kotlin we use SomeClass::class and someInstance::class while class is not a function/method?

println(String::compareTo)
// output: fun kotlin.String.compareTo(kotlin.String): kotlin.Int
println("string".compareTo("strong"))
// output: -6
println(String::class)
// output: class kotlin.String
println("string".class)
// compile error

Upvotes: 53

Views: 29500

Answers (2)

Miha_x64
Miha_x64

Reputation: 6363

:: in Kotlin is about meta-programming, including method references, property references and class literals. See discussion about class literals.

Upvotes: 26

Lior Bar-On
Lior Bar-On

Reputation: 11480

In Kotlin you can write Object::class, which will give you a KClass. KClass is not equivalent to the class Class that we know from Java. If you want to get the Java Class class you can write Object::class.java - i.e.: println("string"::class.java)

Also in java, .class is not a method or a member - it is a special directive for the compiler to access the class. I guess each language select the syntax that makes most sense for it, and kotlin's creators decided to use ::

Upvotes: 53

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