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| import kotlin.reflect.full.declaredMemberProperties | |
| import kotlin.reflect.full.primaryConstructor | |
| /** | |
| * Merge two data classes | |
| * | |
| * The resulting data class will contain: | |
| * - all fields of `other` which are non null | |
| * - the fields of `this` for the fields which are null in `other` | |
| * | |
| * The function is immutable, the original data classes are not changed | |
| * and a new data class instance is returned. | |
| * | |
| * Example usage: | |
| * | |
| * val a = MyDataClass(...) | |
| * val b = MyDataClass(...) | |
| * val c = a merge b | |
| */ | |
| infix inline fun <reified T : Any> T.merge(other: T): T { | |
| val nameToProperty = T::class.declaredMemberProperties.associateBy { it.name } | |
| val primaryConstructor = T::class.primaryConstructor!! | |
| val args = primaryConstructor.parameters.associateWith { parameter -> | |
| val property = nameToProperty[parameter.name]!! | |
| (property.get(other) ?: property.get(this)) | |
| } | |
| return primaryConstructor.callBy(args) | |
| } |
@talatkuyuk this logic captured in the line:
parameter to (property.get(other) ?: property.get(this))
Right now the behavior is: take the property from other, but if that is null, take the property from from this.
You can adjust the exact behavior of when to pick a property from either other or this as you like, i.e. add an extra conditional check to pick other only when it is non null and not zero (when it is a numeric value).
@josdejong Thank you very much. I understand it, but I am new in Kotlin. I am not familiar with to operator. I didn't write any inflix function yet. Just I needed this.
- The resulting data class will contain:
-
- all fields of
otherwhich are non null or non Double with value 0.0
- all fields of
-
- the fields of
thisfor the fields which are null or Double with value 0.0 inother
- the fields of
I tried to make it, I am stuck.
Something like this - just change the exact logic to meet your needs (and think through what logic you need for Double, Float, Int. etc, there may be a smart way to check whether any numeric type is zero, I don't know):
infix inline fun <reified T : Any> T.mergeIgnoreZero(other: T): T {
val nameToProperty = T::class.declaredMemberProperties.associateBy { it.name }
val primaryConstructor = T::class.primaryConstructor!!
val args = primaryConstructor.parameters.associateWith { parameter ->
val property = nameToProperty[parameter.name]!!
val valueOther = property.get(other)
val valueThis = property.get(this)
if (valueOther is Double && valueOther == 0.0) {
valueThis
} else {
valueOther ?: valueThis
}
}
return primaryConstructor.callBy(args)
}
@josdejong Thank you very much. It worked.
👍
How can I add extra condition, for example:
otherwhich are non null or zerothisfor the fields which are null or zero inotheror
otherwhich are non null or Double 0.0thisfor the fields which are null or Double 0.0 inotherWhich line I have to put this kind of conditions?