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package kotlin.properties
import java.util.NoSuchElementException
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)
}
/**
* Returns a property delegate for a read/write property that stores its value in a map, using the property name
* as a key.
* @param map the map where the property values are stored.
*/
@Deprecated("Delegate property to the map itself without creating a wrapper.", ReplaceWith("map", "kotlin.properties.get", "kotlin.properties.set"))
public fun mapVar(map: MutableMap): ReadWriteProperty {
return FixedMapVar(map, propertyNameSelector, throwKeyNotFound)
}
/**
* Returns a property delegate for a read/write property that stores its value in a map, using the property name
* as a key.
* @param map the map where the property values are stored.
* @param default the function returning the value of the property for a given object if it's missing from the given map.
*/
public fun mapVar(map: MutableMap,
default: (thisRef: Any?, desc: String) -> T): ReadWriteProperty {
return FixedMapVar(map, propertyNameSelector, default)
}
/**
* Returns a property delegate for a read-only property that takes its value from a map, using the property name
* as a key.
* @param map the map where the property values are stored.
*/
@Deprecated("Delegate property to the map itself without creating a wrapper.", ReplaceWith("map", "kotlin.properties.get"))
public fun mapVal(map: Map): ReadOnlyProperty {
return FixedMapVal(map, propertyNameSelector, throwKeyNotFound)
}
/**
* Returns a property delegate for a read-only property that takes its value from a map, using the property name
* as a key.
* @param map the map where the property values are stored.
* @param default the function returning the value of the property for a given object if it's missing from the given map.
*/
public fun mapVal(map: Map,
default: (thisRef: Any?, desc: String) -> T): ReadOnlyProperty {
return FixedMapVal(map, propertyNameSelector, default)
}
}
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
}
}
/**
* Implements the core logic of a property delegate for a read/write property that calls callback functions when changed.
* @param initialValue the initial value of the property.
*/
public abstract class ObservableProperty(initialValue: T) : ReadWriteProperty {
private var value = initialValue
/**
* 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.
*/
protected open fun beforeChange(property: KProperty<*>, oldValue: T, newValue: T): Boolean = true
/**
* 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.
*/
protected open fun afterChange (property: KProperty<*>, oldValue: T, newValue: T): Unit {}
public override fun getValue(thisRef: Any?, property: KProperty<*>): T {
return value
}
public override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
val oldValue = this.value
if (!beforeChange(property, oldValue, value)) {
return
}
this.value = value
afterChange(property, oldValue, value)
}
}
/**
* Implements the core logic for a property delegate that stores property values in a map.
* @param T the type of the object that owns the delegated property.
* @param K the type of key in the map.
* @param V the type of the property value.
*/
public abstract class MapVal() : ReadOnlyProperty {
/**
* Returns the map used to store the values of the properties of the given object instance.
* @param ref the object instance for which the map is requested.
*/
protected abstract fun map(ref: T): Map
/**
* Returns the map key used to store the values of the given property.
* @param property the property for which the key is requested.
*/
protected abstract fun key(property: KProperty<*>): K
/**
* Returns the property value to be used when the map does not contain the corresponding key.
* @param ref the object instance for which the value was requested.
* @param property the property for which the value was requested.
*/
protected open fun default(ref: T, property: KProperty<*>): V {
throw NoSuchElementException("The value for property ${property.name} is missing in $ref.")
}
public override fun getValue(thisRef: T, property: KProperty<*>) : V {
val map = map(thisRef)
val key = key(property)
return map.getOrElse(key, { default(thisRef, property) }) as V
}
}
/**
* Implements the core logic for a read/write property delegate that stores property values in a map.
* @param T the type of the object that owns the delegated property.
* @param K the type of key in the map.
* @param V the type of the property value.
*/
public abstract class MapVar() : MapVal(), ReadWriteProperty {
protected abstract override fun map(ref: T): MutableMap
public override fun setValue(thisRef: T, property: KProperty<*>, value: V) {
val map = map(thisRef)
map.put(key(property), value)
}
override fun getValue(thisRef: T, property: KProperty<*>): V {
return super.getValue(thisRef, property)
}
}
private val propertyNameSelector: (KProperty<*>) -> String = {it.name}
private val throwKeyNotFound: (Any?, Any?) -> Nothing = {thisRef, key -> throw NoSuchElementException("The value for key $key is missing from $thisRef.") }
/**
* Implements a read-only property delegate that stores the property values in a given map instance and uses the given
* callback functions for calculating the key and the default value for each property.
* @param map the map used to store the values.
* @param key the function to calculate the map key from a property metadata object.
* @param default the function returning the value of the property for a given object if it's missing from the given map.
*/
public open class FixedMapVal(
private val map: Map,
private val key: (KProperty<*>) -> K,
private val default: (ref: T, key: K) -> V = throwKeyNotFound
) : MapVal() {
protected override fun map(ref: T): Map {
return map
}
protected override fun key(property: KProperty<*>): K {
return (key)(property)
}
protected override fun default(ref: T, property: KProperty<*>): V {
return (default)(ref, key(property))
}
}
/**
* Implements a read/write property delegate that stores the property values in a given map instance and uses the given
* callback functions for calculating the key and the default value for each property.
* @param map the map used to store the values.
* @param key the function to calculate the map key from a property metadata object.
* @param default the function returning the value of the property for a given object if it's missing from the given map.
*/
public open class FixedMapVar(
private val map: MutableMap,
private val key: (KProperty<*>) -> K,
private val default: (ref: T, key: K) -> V = throwKeyNotFound
) : MapVar() {
protected override fun map(ref: T): MutableMap {
return map
}
protected override fun key(property: KProperty<*>): K {
return (key)(property)
}
protected override fun default(ref: T, property: KProperty<*>): V {
return (default)(ref, key(property))
}
}
