for case let val? in values {
print("Value in values is (val)")
}
或者：
valuesIterator = values.makeIterator()
while let val = valuesIterator.next(), val != nil {
print("Value in values is (String(describing: val))")
}
这样就可以将 nil 值给过滤了，是不是很简单？还可以使用 for case 匹配枚举值数组：
let results: [Result] = [.success, .failure]
for case .success in results {
print("Values in results contains success.")
break
}
对于复杂的枚举类型：
enum NetResource {
case http(resource: String)
case ftp(resource: String)
}
let nets: [NetResource] = [.http(resource: "https://www.easck.com//www.apple.cn"), .ftp(resource: ftp://192.0.0.1)]
过滤 http 的值：
for case .http(let resource) in nets {
print("HTTP resource (resource)")
}
for 循环使用 where 从句
除此之外，我们还可以在 for 循环后边跟上一个 where 从句来进行模式匹配：
for notNilValue in values where notNilValue != nil {
print("Not nil value: (String(describing: notNilValue!))")
}
查询一个数组里边所有能被3整除的数：
let rangeValues = Array(0...999)
for threeDivideValue in rangeValues where threeDivideValue % 3 == 0 {
print("Three devide value: (threeDivideValue)")
}
查询所有含有3的数：
for containsThree in rangeValues where String(containsThree).contains("3") {
print("Value contains three: (containsThree)")
}
