Scope Resolution Operator in Kotlin

Question

I have read the following syntax. I have no idea why scope resolution operator is used in it.

class XyzFragment : Fragment() {

    lateinit var adapter: ChatAdapter

    override fun onViewCreated(view: View?, savedInstanceState: Bundle?) {
        if (!::adapter.isInitialized) { <-- This one
            adapter = ChatAdapter(this, arrayListOf())
        }
    }
}

I want to know what is :: in if (!::adapter.isInitialized) { statement.

FYI, trying to compile this in Kotlin <1.2 gives a pretty descriptive error message of what it is. kotlinlang.org/docs/reference/whatsnew12.html — Qaz
– Qaz, Commented Dec 20, 2017 at 6:07

Joshua · Accepted Answer · 2017-12-20 07:15:33Z

6

:: is a short form for this:: in Kotlin.

:: is a operator to creates a member reference or a class reference. For example,

class Test {        
    fun foo() {

    }

    fun foo2(value: Int) {

    }

    fun bar() {
        val fooFunction = ::foo
        fooFunction.invoke()  // equals to this.foo()
        val foo2Function = ::foo2
        foo2Function.invoke(1)  // equals to this.foo2(1)
        val fooFunction2 = Test::foo
        val testObject = Test()
        fooFunction2.invoke(this) // equals to this.foo()
        fooFunction2.invoke(testObject) // equals to testObject.foo()
    }
}

This is mainly used in reflection and passing function.

edited Dec 20, 2017 at 7:15

answered Dec 20, 2017 at 7:05

Joshua

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2 Comments

Vishnu Haridas Over a year ago

Is it still called a "scope resolution" operator? Couldn't see that name anywhere in the documentation.

Joshua Over a year ago

@VishnuHaridas No, because it never call like that. Here may be what you needed. Also, you should ask a new question instead of writing comment.

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