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var languages = ["Swift", "Objective-C"]
contains(languages, "Swift") == true
contains(languages, "Java") == false
contains([29, 85, 42, 96, 75], 42) == true
dropFirst(sequence)：返回一个去掉了首个元素的、新的序列（比如一个新数组）。
复制代码var languages = ["Swift", "Objective-C"]
var oldLanguages = dropFirst(languages)
equal(oldLanguages, ["Objective-C"]) == true
dropLast(sequence)：返回一个去掉了最后一个元素的、新的序列（比如一个新数组）。
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var languages = ["Swift", "Objective-C"]
var newLanguages = dropLast(languages)
equal(newLanguages, ["Swift"]) == true
dump(object)：打印出某个对象object的所有信息
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var languages = ["Swift", "Objective-C"]
dump(languages)
// Prints:
// ▿ 2 elements
// - [0]: Swift
// - [1]: Objective-C
equal(sequence1, sequence2)：判断两个序列是否相等
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var languages = ["Swift", "Objective-C"]
equal(languages, ["Swift", "Objective-C"]) == true
var oldLanguages = dropFirst(languages)
equal(oldLanguages, ["Objective-C"]) == true
filter(sequence, includeElementClosure)：对序列sequence中每个元素都执行includeElementClosure闭包，并将所有闭包结果为true的元素合成一个新序列sequence并返回。
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for i in filter(1...100, { $0 % 10 == 0 }) {
// 10, 20, 30, ...
println(i)
assert(contains([10, 20, 30, 40, 50, 60, 70, 80, 90, 100], i))
}
find(sequence, element)：返回序列sequence中某元素element的位置index。如果序列中不存在此元素，则返回nil。
