fix 3.7 patterns
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stanzhai
@ -1,6 +1,5 @@
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> 翻译：honghaoz
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> 校对：numbbbbb, stanzhai
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> 翻译：honghaoz
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> 校对：numbbbbb, stanzhai
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# 模式（Patterns）
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-----------------
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@ -35,9 +34,11 @@
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通配符模式匹配并忽略任何值，包含一个下划线（_）。当你不关心被匹配的值时，可以使用此模式。例如，下面这段代码进行了`1...3`的循环，并忽略了每次循环的值：
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for _ in 1...3 {
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// Do something three times.
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}
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```swift
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for _ in 1...3 {
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// Do something three times.
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}
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```
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> 通配符模式语法
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> *通配符模式* → **_**
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@ -47,7 +48,9 @@
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标识符模式匹配任何值，并将匹配的值和一个变量或常量绑定起来。例如，在下面的常量申明中，`someValue`是一个标识符模式，匹配了类型是`Int`的`42`。
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let someValue = 42
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```swift
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let someValue = 42
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```
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当匹配成功时，`42`被绑定（赋值）给常量`someValue`。
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@ -63,13 +66,15 @@
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标识符模式包含在值绑定模式中，绑定新的变量或常量到匹配的值。例如，你可以分解一个元组的元素，并把每个元素绑定到相应的标识符模式中。
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let point = (3, 2)
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switch point {
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// Bind x and y to the elements of point.
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case let (x, y):
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println("The point is at (\(x), \(y)).")
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}
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// prints "The point is at (3, 2).”
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```swift
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let point = (3, 2)
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switch point {
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// Bind x and y to the elements of point.
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case let (x, y):
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println("The point is at (\(x), \(y)).")
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}
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// prints "The point is at (3, 2).”
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```
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在上面这个例子中，`let`将元组模式`(x, y)`分配到各个标识符模式。因为这种行为，`switch`语句中`case let (x, y):`和`case (let x, let y):`匹配的值是一样的。
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@ -85,17 +90,21 @@
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当元组模式被用在`for-in`语句或者变量或常量申明时，它可以包含通配符模式，标识符模式或者其他包含这两种模式的模式。例如，下面这段代码是不正确的，因为`(x, 0)`中的元素`0`是一个表达式模式：
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let points = [(0, 0), (1, 0), (1, 1), (2, 0), (2, 1)]
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// This code isn't valid.
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for (x, 0) in points {
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/* ... */
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}
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```swift
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let points = [(0, 0), (1, 0), (1, 1), (2, 0), (2, 1)]
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// This code isn't valid.
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for (x, 0) in points {
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/* ... */
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}
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```
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对于只包含一个元素的元组，括号是不起作用的。模式匹配那个单个元素的类型。例如，下面是等效的：
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let a = 2 // a: Int = 2
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let (a) = 2 // a: Int = 2
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let (a): Int = 2 // a: Int = 2
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```swift
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let a = 2 // a: Int = 2
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let (a) = 2 // a: Int = 2
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let (a): Int = 2 // a: Int = 2
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```
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> 元组模式语法
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> *元组模式* → **(** [*元组模式元素列表*](..\chapter3\07_Patterns.html#tuple_pattern_element_list) _可选_ **)**
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@ -117,8 +126,8 @@
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有两种类型转换模式，`is`模式和`as`模式。这两种模式均只出现在`switch`语句中的`case`标签中。`is`模式和`as`模式有以下形式：
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is type
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pattern as type
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> is `type`
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> `pattern` as `type`
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`is`模式匹配一个值，如果这个值的类型在运行时（runtime）和`is`模式右边的指定类型（或者那个类型的子类）是一致的。`is`模式和`is`操作符一样，它们都进行类型转换，但是抛弃了返回的类型。
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@ -138,33 +147,36 @@
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由表达式模式所代表的表达式用Swift标准库中的`~=`操作符与输入表达式的值进行比较。如果`~=`操作符返回`true`，则匹配成功。默认情况下，`~=`操作符使用`==`操作符来比较两个相同类型的值。它也可以匹配一个整数值与一个`Range`对象中的整数范围，正如下面这个例子所示：
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let point = (1, 2)
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switch point {
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case (0, 0):
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println("(0, 0) is at the origin.")
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case (-2...2, -2...2):
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println("(\(point.0), \(point.1)) is near the origin.")
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default:
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println("The point is at (\(point.0), \(point.1)).")
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}
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// prints "(1, 2) is near the origin.”
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```swift
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let point = (1, 2)
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switch point {
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case (0, 0):
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println("(0, 0) is at the origin.")
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case (-2...2, -2...2):
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println("(\(point.0), \(point.1)) is near the origin.")
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default:
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println("The point is at (\(point.0), \(point.1)).")
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}
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// prints "(1, 2) is near the origin.”
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```
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你可以重载`~=`操作符来提供自定义的表达式行为。例如，你可以重写上面的例子，以实现用字符串表达的点来比较`point`表达式。
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// Overload the ~= operator to match a string with an integer
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func ~=(pattern: String, value: Int) -> Bool {
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return pattern == "\(value)"
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}
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switch point {
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case ("0", "0"):
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println("(0, 0) is at the origin.")
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case ("-2...2", "-2...2"):
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println("(\(point.0), \(point.1)) is near the origin.")
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default:
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println("The point is at (\(point.0), \(point.1)).")
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}
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// prints "(1, 2) is near the origin.”
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```swift
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// Overload the ~= operator to match a string with an integer
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func ~=(pattern: String, value: Int) -> Bool {
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return pattern == "\(value)"
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}
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switch point {
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case ("0", "0"):
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println("(0, 0) is at the origin.")
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case ("-2...2", "-2...2"):
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println("(\(point.0), \(point.1)) is near the origin.")
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default:
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println("The point is at (\(point.0), \(point.1)).")
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}
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// prints "(1, 2) is near the origin.”
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```
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> 表达式模式语法
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> *表达式模式* → [*表达式*](..\chapter3\04_Expressions.html#expression)
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> *表达式模式* → [*表达式*](..\chapter3\04_Expressions.html#expression)
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