I can't understand source code implementation of string.kt in kotlin

Question

In kotlin source code, I can't understand how to implement of length of String.kt , it is as following:

package kotlin                                                  
public class String : Comparable<String>, CharSequence {
companion object {}

/**
 * Returns a string obtained by concatenating this string with the string representation of the given [other] object.
 */
public operator fun plus(other: Any?): String

public override val length: Int

public override fun get(index: Int): Char

public override fun subSequence(startIndex: Int, endIndex: Int): CharSequence

public override fun compareTo(other: String): Int}

var len:Int = "abc".length; // len = 3 where to run the length??

where to implement the length function?

when you write this `"abc".length` and in return you want lenght of string? — Patel Pinkal, Jun 13 '17 at 14:00
yeah, I can get the correct result. I just want to know where to implement in kotlin source code . I have added the String.kt above. — Jim Green, Jun 14 '17 at 01:30

score 13 · Answer 1 · answered Jun 13 '17 at 14:15

13

The string functions are examples of what Kotlin considers Intrinsic functions. They are defined based on the platform they are running on and you won't be able to find an implementation of them in the source code.

For the JVM they will be directly mapped to the corresponding native java.lang.String methods. This ensures there is no runtime overhead and leverages the optimizations done in the java standard library.

answered Jun 13 '17 at 14:15

Kiskae

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There are no 'implementations', when those functions are called the compiler does some custom code generation to produce the result. Some of the mapped functions can be found at https://github.com/JetBrains/kotlin/blob/master/compiler/backend/src/org/jetbrains/kotlin/codegen/intrinsics/IntrinsicMethods.java – Kiskae Jun 15 '17 at 13:49

I can't understand source code implementation of string.kt in kotlin

1 Answers1