Move extension functions to interface itself, add box() GetterSetter

src/main/kotlin/ru/dbotthepony/mc/otm/core/GetterSetter.kt

@@ -27,6 +27,35 @@ interface GetterSetter<V> : Supplier<V>, Consumer<V>, ReadWriteProperty<Any?, V>
 		accept(value)
 	}
 
+	fun asGetterOnly(): GetterSetter<V> {
+		val self = this
+
+		return object : GetterSetter<V> {
+			override fun get(): V {
+				return self.get()
+			}
+
+			override fun accept(t: V) {
+			}
+		}
+	}
+
+	fun watch(watch: (old: V, new: V) -> Unit): GetterSetter<V> {
+		val self = this
+
+		return object : GetterSetter<V> {
+			override fun get(): V {
+				return self.get()
+			}
+
+			override fun accept(t: V) {
+				val old = get()
+				self.accept(t)
+				watch.invoke(old, t)
+			}
+		}
+	}
+
 	companion object {
 		fun <V> of(getter: Supplier<V>, setter: Consumer<V>): GetterSetter<V> {
 			return object : GetterSetter<V> {
@@ -63,6 +92,20 @@ interface GetterSetter<V> : Supplier<V>, Consumer<V>, ReadWriteProperty<Any?, V>
 				}
 			}
 		}
+
+		fun <V> box(value: V): GetterSetter<V> {
+			return object : GetterSetter<V> {
+				private var value = value
+
+				override fun get(): V {
+					return value
+				}
+
+				override fun accept(t: V) {
+					this.value = t
+				}
+			}
+		}
 	}
 }
 
@@ -84,18 +127,4 @@ fun <V> KMutableProperty0<V>.asGetterSetter(watch: ((old: V, new: V) -> Unit)? =
 	}
 }
 
-fun <V> GetterSetter<V>.watch(watch: (old: V, new: V) -> Unit): GetterSetter<V> {
-	return object : GetterSetter<V> {
-		override fun get(): V {
-			return this@watch.get()
-		}
-
-		override fun accept(t: V) {
-			val old = get()
-			this@watch.accept(t)
-			watch.invoke(old, t)
-		}
-	}
-}
-
 fun <V> KMutableProperty0<V>.asGetterOnly() = GetterSetter.of(Supplier { this.get() }, Consumer { /* do nothing */ })