swift 之 map

map基本使用方法：@H_403_2@

@H_403_2@

var@H_403_2@ xa = [@H_403_2@1@H_403_2@,@H_403_2@2@H_403_2@,@H_403_2@3@H_403_2@]@H_403_2@

let@H_403_2@ squares =@H_403_2@xa@H_403_2@.@H_403_2@map@H_403_2@ {@H_403_2@@H_403_2@

$0 * $0@H_403_2@

}@H_403_2@

等价于：@H_403_2@

@H_403_2@

var@H_403_2@ squares = [@H_403_2@Int@H_403_2@]()@H_403_2@

for@H_403_2@ e @H_403_2@in@H_403_2@ @H_403_2@xa@H_403_2@ {@H_403_2@

@H_403_2@squares@H_403_2@.@H_403_2@append@H_403_2@(e * e)@H_403_2@

}@H_403_2@

map的实现方法：@H_403_2@

extension@H_403_2@ @H_403_2@Array@H_403_2@ {@H_403_2@

@H_403_2@func@H_403_2@ map_wershest<T>(@H_403_2@_@H_403_2@ transform:(@H_403_2@Element@H_403_2@)->@H_403_2@T@H_403_2@) -> [@H_403_2@T@H_403_2@] {@H_403_2@

@H_403_2@var@H_403_2@ result: [@H_403_2@T@H_403_2@] = []@H_403_2@

result.@H_403_2@reserveCapacity@H_403_2@(@H_403_2@count@H_403_2@)@H_403_2@

@H_403_2@for@H_403_2@@H_403_2@x@H_403_2@@H_403_2@in@H_403_2@@H_403_2@self@H_403_2@ {@H_403_2@

result.@H_403_2@append@H_403_2@(transform(x))@H_403_2@

}@H_403_2@

@H_403_2@return@H_403_2@ result@H_403_2@

}@H_403_2@

@H_403_2@

let@H_403_2@ cubes = @H_403_2@x@H_403_2@.@H_403_2@map_wershest@H_403_2@ {@H_403_2@

$0 * $0 * $0@H_403_2@

}@H_403_2@

@H_403_2@

不禁回想起十多年前，第一次遇见C++标准库，一脸懵x。硬着头皮看了几眼，掉头就走，再也没有回去过。

如此简单的“套路”，居然成为了大名鼎鼎的 map-reduce。

现在想想，当时只是少了一点点耐心，再加上英语单词背的太少，无法找到循序渐进的书籍，由浅入深的把它学透。

以至于，与如此简单而神奇的代码，错过了十多年。

感谢万能的Internet，如今我们可以轻易的薅资本主义羊毛：

<Eloquent JavaScript,2nd Edition> (safaribooksonline.com),Chapter 5. Higher-Order Functions

<Mastering Swift 3> (safaribooksonline.com),Chapter 3. Using Swift Collections and the Tuple Type

<Advanced Swift> Chapter 1 Built-In Collections

原文链接：https://www.f2er.com/swift/322060.html

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