KotlinDeepCopy

Introduction: DeepCopy extensions and apt for Kotlin Data class.
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This is a demo for JetBrains Open Day 2018 in Beijing.

Provide an easy way to generate DeepCopy function for data class. DeepCopy only takes effect on the component members i.e. the members declared in the primary constructor.

Reflection

Use Kotlin Reflection to provide an extension function for Any so that any data class can simple call deepCopy() to copy itsself.

See the test code below:

data class Speaker(val name: String, val age: Int)

data class Talk(val name: String, val speaker: Speaker)

class DeepCopyTest {
    @Test
    fun test() {
        val talk = Talk("DataClass in Action", Speaker("Benny Huo", 30))
        val newTalk = talk.deepCopy()
        assert(talk == newTalk)
        assert(talk !== newTalk)
    }
}

talk equals newTalk since the values of their members are equal while they do not ref to the same object.

How to Setup

This library has been deloyed to jcenter.

compile 'com.bennyhuo.kotlin:deepcopy-reflect:1.0'

Apt

If you concern about the runtime efficiency, apt may be the solution. You can simply annotate the data class you want to deep copy with a DeepCopy annotation:

@DeepCopy
data class Speaker(val name: String, val age: Int)
@DeepCopy
data class Talk(val name: String, val speaker: Speaker)

Extension function deepCopy will be generated according to the components:

fun Talk.deepCopy(): Talk = Talk(name, speaker.deepCopy())

fun Speaker.deepCopy(): Speaker = Speaker(name, age)

Notice that deepCopy is called recursively if the member type is also a data class annotated with a DeepCopy annotation. Hence, if you remove the annotation for Speaker, generated function would be like:

fun Talk.deepCopy(): Talk = Talk(name, speaker)

//And no deepCopy for Speaker.

How to Setup

This library has been deloyed to jcenter, but the compiler depends on the experimental artifact kotlinx-metadata-jvm so you should also add a maven repo https://kotlin.bintray.com/kotlinx/ to compile.


repositories {
    jcenter()
    maven { url "https://kotlin.bintray.com/kotlinx/" }
}

...
apply plugin: "kotlin-kapt"
...

dependencies {
    kapt 'com.bennyhuo.kotlin:deepcopy-compiler:1.0'
    compile 'com.bennyhuo.kotlin:deepcopy-annotations:1.0'
}

License

MIT License

Copyright (c) 2018 Bennyhuo

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
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