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Update ch17-03-oo-design-patterns.md

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Zheng Ping 2017-06-07 18:01:14 +08:00 committed by GitHub
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@ -69,15 +69,9 @@ struct Draft {}
impl State for Draft {}
```
<span class="caption">Listing 17-12: Definition of a `Post` struct and a `new`
function that creates a new `Post` instance, a `State` trait, and a `Draft`
struct that implements `State`</span>
<span class="caption">列表17-12: 定义一个`Post`结构, 一个`Post`结构的创建一个新的`Post`实例的关联函数`new`, 一个`State`trait, 和一个实现了`State`的结构`Draft`.</span>
When we create a new `Post`, we set its `state` field to a `Some` value holding
a `Box` pointing to a new instance of the `Draft` struct. This ensures whenever
we create a new instance of `Post`, it'll start out as a draft. Because the
`state` field of `Post` is private, there's no way to create a `Post` in any
other state!
当我们创建一个新的`Post`实例时, 我们把它的`state`字段设为一个持有指向一个新的`Draft`结构实例的`Box`的`Some`类型的值. 这就确保无论何时我们创建一个`Post`类型的新实例时, 它总是处于草稿状态. 因为`Post`的`state`字段是私有的, 也就没有办法创建一个处于其它状态的`Post`!
### Storing the Text of the Post Content