使用（Object as TClass）和TClass（Object）之间有什么区别？ [英] What's the difference between casting using (Object as TClass) and TClass(Object)

问题描述

有一个问题，其中 MyObj.classnameis（TMyClass.classname）为true， TMyClass（MyObj） （MyObj as TMyclass）.doSomething 引发转换错误。

Got an issue where MyObj.classnameis(TMyClass.classname) is true and TMyClass(MyObj) works but (MyObj as TMyclass).doSomething throws a conversion error.

我真的不想帮助那些垃圾，虽然如果你想把它放在评论中是超级的。我只想知道 Obj之间的区别 和 Class（Obj） 是。

I don't really want any help with that junk, although if you want to put it in the comments that'd be super. I just would like to know what the difference between Obj as Class and Class(Obj) is.

推荐答案

铸件检查实际对象类型，有效，如果不是，则引发异常。 hard cast（ TMyClass（MyObj） style）不检查，它只是告诉编译器假设转换是有效的。

An as-cast checks the actual object type to make sure the cast is valid, and raises an exception if it's not. A "hard cast" (TMyClass(MyObj) style) does not check, it just tells the compiler to assume the cast is valid.

如果你有一个情况，ClassNameIs返回true但as-cast失败，这意味着你有两个不同的类在两个不同的单位具有相同的名称，并且as-cast试图转换错了一个。

If you've got a situation where ClassNameIs returns true but the as-cast fails, that means you have two different classes in two different units with the same name, and the as-cast is trying to cast to the wrong one. This also means that your hard-cast is casting to the wrong one, which could potentially lead to memory corruption.

运行完整的项目搜索TMyclass =可以看到其中你的多个声明是，并重命名其中一个类或使用一个完整的定义（obj作为MyUnit.TMyClass），所以编译器将知道你试图投射到哪个类。

Run a full project search for "TMyclass =" to see where your multiple declarations are, and either rename one of the classes or use a full definition (obj as MyUnit.TMyClass) so the compiler will know which class you're trying to cast to.

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