命名参数和可选参数是两个比较简单的特性，对于熟悉其他编程语言的开发者来说可选参数并不陌生，为参数提供默认值时就是可选参数：
The domain name of the Internet site has long been registered quite a few several years ago. Usually, the older the web site the more honest it turns into. However, scammers occasionally purchase present Internet websites and begin doing their evil matter, so make sure you you should definitely check for other scammy attributes also.
These default folders are not displayed underneath This Laptop to keep the check out focused on your Laptop’s drives and network locations.
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本文提供的工具可用来加密和解密文件，如果你急着给一些文件加密，只需直接启动本文后面提供的工具即可。
协变和逆变，是为解决问题而生的。而要理清解决什么样的问题，需要首先从理清几个简单的概念开始。首先我们进行一点操作：
When File Explorer opens, you are going to land in Swift entry. Your often utilised folders and a short while ago used information are stated there, so you won't must dig through a number of folders to uncover them. Pin your preferred folders to Rapid usage of hold them close at hand.
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而这种原始转换（由子类转换为父类）方向相同的可变性，被称为协变（covariant）；其反向操作则被称为逆变（contravariant）。当同样的情形应用于泛型时，例如：
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