Before moving on to initializer list examples and typical usage, let's look at what is meant by type narrowing.

在研究初始化器列表示例和典型用法之前，先讨论一下什么是类型窄化。

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When you select an environment profile, you can optionally filter the list of available profiles by providing an environment type other than all.

在选择环境概要文件时，通过提供All之外的其他环境类型，可以筛选可用概要文件列表。

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The instanceof function provides a good way of checking type, but you can also roll object type checking into the method signature itself by using type hints in the argument list.

虽然 instanceof 功能提供了一种检查类型的好方法，但您还可以通过在参数列表中使用类型提示，来将对象类型检查滚动到方法签名自身中。

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