kotlin.properties.Delegates.kt Maven / Gradle / Ivy
package kotlin.properties
import kotlin.reflect.KProperty
/**
* Standard property delegates.
*/
public object Delegates {
/**
* Returns a property delegate for a read/write property with a non-`null` value that is initialized not during
* object construction time but at a later time. Trying to read the property before the initial value has been
* assigned results in an exception.
*/
public fun notNull(): ReadWriteProperty = NotNullVar()
/**
* Returns a property delegate for a read/write property that calls a specified callback function when changed.
* @param initialValue the initial value of the property.
* @param onChange the callback which is called after the change of the property is made. The value of the property
* has already been changed when this callback is invoked.
*/
public inline fun observable(initialValue: T, crossinline onChange: (property: KProperty<*>, oldValue: T, newValue: T) -> Unit):
ReadWriteProperty = object : ObservableProperty(initialValue) {
override fun afterChange(property: KProperty<*>, oldValue: T, newValue: T) = onChange(property, oldValue, newValue)
}
/**
* Returns a property delegate for a read/write property that calls a specified callback function when changed,
* allowing the callback to veto the modification.
* @param initialValue the initial value of the property.
* @param onChange the callback which is called before a change to the property value is attempted.
* The value of the property hasn't been changed yet, when this callback is invoked.
* If the callback returns `true` the value of the property is being set to the new value,
* and if the callback returns `false` the new value is discarded and the property remains its old value.
*/
public inline fun vetoable(initialValue: T, crossinline onChange: (property: KProperty<*>, oldValue: T, newValue: T) -> Boolean):
ReadWriteProperty = object : ObservableProperty(initialValue) {
override fun beforeChange(property: KProperty<*>, oldValue: T, newValue: T): Boolean = onChange(property, oldValue, newValue)
}
}
private class NotNullVar() : ReadWriteProperty {
private var value: T? = null
public override fun getValue(thisRef: Any?, property: KProperty<*>): T {
return value ?: throw IllegalStateException("Property ${property.name} should be initialized before get.")
}
public override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
this.value = value
}
}