重載遵守變異（第3.4節）的規則。也就是說，它們的參數類型允許逆變（不那么特定的類型）而它們的返回類型允許共變（更特別的類型）。 > Overriding adheres to the rules of variance (3.4). That is, their argument types allow contravariance (less speci?c types) while their return type allows covariance (more speci?c types): ~~~ class Base { public function new() { } } class Child extends Base { private function method(obj:Child):Child { return obj; } } class ChildChild extends Child { public override function method(obj:Base):ChildChild { return null; } } class Main { static public function main() { } } ~~~ 直觀的說，這是因為參數被“寫入”到函數中，而返回值是從函數中“讀取”。 > Intuitively, this follows from the fact that arguments are “written to” the function and the return value is “read from” it. 示例也展示了如何改變可見性（第4.4.1節）：一個重載的字段可能是 public ，如果被重載的字段是private，但是相反則不行。 > The example also demonstrates how visibility (4.4.1) may be changed: An overriding ?eld may be public if the overridden ?eld is private, but not the other way around. 不可能重載聲明為內聯（第4.4.2節）的字段。這是由于沖突的概念：當內聯在編譯時通過替換一個函數體的調用，重載字段必須被在運行時決定。 > It is not possible to override ?elds which are declared as inline (4.4.2). This is due to the con?icting concepts: While inlining is done atcompile-time by replacinga call with thefunction body, overriding ?elds necessarily have to be resolved at runtime.