delegate by map

When to use

Map 을 통해 객체를 생성하고 싶을 때

How to use

info

kotlin Map already implements method for delegating.

Project.kt

Use by map on property.

Project.kt

data class Project(val map: MutableMap<String, Any?>) {
    var name: String by map
    var priority: Int by map
    var completed: Boolean by map
}

ProjectTest.kt

class ProjectTest {
    @DisplayName("Map 으로 project 인스턴스 생성")
    @Test
    internal fun createProjectByMap() {
        val map = mutableMapOf(
            "name" to "Falcon",
            "priority" to 5,
            "completed" to true
        )
        // construction with map
        val project = Project(map)
    }

    @DisplayName("JSON parsing and create project")
    @Test
    internal fun createProjectFromJson() {
        val project = Project(getMapFromDummyJson())
        print(project)
    }
    
    private fun getMapFromDummyJson(): MutableMap<String, Any?> {
        return Gson().fromJson<MutableMap<String, Any?>>(
            """{ "name" : "Learn Kotlin", "priority": 5, "completed": true}""",
            MutableMap::class.java
        )
    }
}

Furthermore

We can support value - based constructor and by map as shown below

data class Project(val map: MutableMap<String, Any?>) {
    var name: String by map
    var priority: Int by map
    var completed: Boolean by map

    constructor(name: String, priority: Int, completed: Boolean) : this(
        mutableMapOf(
            "name" to name,
            "priority" to priority,
            "completed" to completed
        )
    )
}

@DisplayName("create json with property value")
@Test
internal fun createProjectWithPropValue() {
    print(Project("카르마", 5, true))
}