给定一个键类型为字符串的字典Dictionary
,有没有一种方式以不区分大小写的方式访问其值?例如:
let dict = [
"name": "John",
"location": "Chicago"
]
有没有一种方法可以调用dict["NAME"], dict["nAmE"]
等,仍然得到"John"
?
更简洁的方法,Swift 4:
extension Dictionary where Key == String {
subscript(caseInsensitive key: Key) -> Value? {
get {
if let k = keys.first(where: { $0.caseInsensitiveCompare(key) == .orderedSame }) {
return self[k]
}
return nil
}
set {
if let k = keys.first(where: { $0.caseInsensitiveCompare(key) == .orderedSame }) {
self[k] = newValue
} else {
self[key] = newValue
}
}
}
}
// Usage:
var dict = ["name": "John"]
dict[caseInsensitive: "NAME"] = "David" // overwrites "name" value
print(dict[caseInsensitive: "name"]!) // outputs "David"
Swift支持多个下标,因此您可以利用这一点来定义不区分大小写的访问器:
extension Dictionary where Key : StringLiteralConvertible {
subscript(ci key : Key) -> Value? {
get {
let searchKey = String(key).lowercaseString
for k in self.keys {
let lowerK = String(k).lowercaseString
if searchKey == lowerK {
return self[k]
}
}
return nil
}
}
}
// Usage:
let dict = [
"name": "John",
"location": "Chicago",
]
print(dict[ci: "NAME"]) // John
print(dict[ci: "lOcAtIoN"]) // Chicago
这个扩展仅适用于键类型为String
的Dictionary
(因为小写形式对于其他数据类型是没有意义的)。然而,Swift会抱怨将泛型类型限制为struct
。最接近String
的协议是StringLiteralConvertible
。
请注意,如果您有两个小写形式相同的键,则不能保证您将得到哪一个:
let dict = [
"name": "John",
"NAME": "David",
]
print(dict[ci: "name"]) // no guarantee that you will get David or John.
/// Wrapper around String which uses case-insensitive implementations for Hashable
public struct CaseInsensitiveString: Hashable, LosslessStringConvertible, ExpressibleByStringLiteral {
public typealias StringLiteralType = String
private let value: String
private let caseInsensitiveValue: String
public init(stringLiteral: String) {
self.value = stringLiteral
self.caseInsensitiveValue = stringLiteral.lowercased()
}
public init?(_ description: String) {
self.init(stringLiteral: description)
}
public var hashValue: Int {
return self.caseInsensitiveValue.hashValue
}
public static func == (lhs: CaseInsensitiveString, rhs: CaseInsensitiveString) -> Bool {
return lhs.caseInsensitiveValue == rhs.caseInsensitiveValue
}
public var description: String {
return value
}
}
var dict = [CaseInsensitiveString: String]()
dict["name"] = "John"
dict["NAME"] = "David" // overwrites "name" value
print(dict["name"]!) // outputs "David"
Collection的first(where:)
方法从所有键值映射中找到第一个小写匹配项,然后返回此结果对应的值。extension Dictionary where Key == String {
func valueForKeyInsensitive<T>(key: Key) -> T? {
let foundKey = self.keys.first { $0.compare(key, options: .caseInsensitive) == .orderedSame } ?? key
return self[foundKey] as? T
}
}
first(where:)
是一种更加高效的过滤或遍历大型集合的方法。struct CaseInsensitiveString<T: StringProtocol>: Hashable, Equatable, CustomStringConvertible {
var string: T
init(_ string: T) {
self.string = string
}
var description: String { get {
return string.description
}}
var hashValue: Int { get {
string.lowercased().hashValue
} }
func hash(into hasher: inout Hasher) {
hasher.combine(hashValue)
}
static func == (lhs: Self, rhs: Self) -> Bool {
return lhs.string.compare(rhs.string, options: .caseInsensitive) == .orderedSame
}
}
typealias SubstringCI = CaseInsensitiveString<String>
var codeMap = [SubstringCI: Int]()
let test = "Abc Def Ghi"
let testsub = test[test.firstIndex(of: "D")!...test.lastIndex(of: "f")!]
codeMap[SubstringCI(String(testsub))] = 1
print(codeMap.keys, codeMap[SubstringCI("Def")]!, codeMap[SubstringCI("def")]!)
codeMap[SubstringCI("DEF")] = 1
print(codeMap.keys, codeMap[SubstringCI("Def")]!, codeMap[SubstringCI("def")]!)
var dict = ["name": "John", "NAME": "David"]
,而不区分大小写查找的结果将变得不可预测。 - neilgmacy