可以在Swift中创建泛型类型检查功能吗？

Ben Baron 发表于 Dev

本·男爵

我向继承的Web API框架中添加了更好的错误处理。目前，它会进行大量强制转换，一旦数据与预期不符，就会导致崩溃。

我想as!用一个检查类型并在失败时引发异常（带有详细描述）的函数替换所有对的使用。

到目前为止，这是我要做的：

func checkType<T>(type: AnyClass, value: T?, name: String) throws -> T {
    guard let value = value else {
        let message = "[\(name)] Expected \(type), but value was nil"
        throw PlaidsterError.InvalidType(message)
    }

    guard value.dynamicType.self == type else {
        let message = "[\(name)] Expected \(type), but it was an \(value.dynamicType.self) with value: \(value)"
        throw PlaidsterError.InvalidType(message)
    }

    return value
}

但这有多个问题。它只能接受对象类型，如果类不完全匹配则失败（例如，NSString失败，因为它实际上是__NSCFString），并且它不能与任何类型（即String，Int，Double ...）一起使用。

我似乎无法找到的代名词AnyClass为Any值类型，这是第一个问题。而且似乎不可能做类似的事情，value.dynamicType.self is type因为它说那type不是一种类型。

有可能做我想做的事吗？有没有更好的方法来进行这种类型检查，而不会在分析代码中散布大量的样板代码？

我的目标是得到像这样甚至更简单的东西：

public struct PlaidCategory {

    // MARK: Properties
    public let id: String
    public let hierarchy: [String]
    public let type: String

    // MARK: Initialization
    public init(category: [String: Any]) throws {
        id = try checkType(String.self, value: category["id"], name: "id")
        hierarchy = try checkType([String].self, value: category["hierarchy"], name: "hierarchy")
        type = try checkType(String.self, value: category["type"], name: "type")
}

}

OOPer

您可以使用另一个泛型类型参数编写类似的内容。

func checkType<T, U>(type: U.Type, value: T?, name: String) throws -> U {
    guard let value = value else {
        let message = "[\(name)] Expected \(type), but value was nil"
        throw PlaidsterError.InvalidType(message)
    }

    guard let result = value as? U else {
        let message = "[\(name)] Expected \(type), but it was an \(value.dynamicType) with value: \(value)"
        throw PlaidsterError.InvalidType(message)
    }

    return result
}

并将其用作：

do {
    let n: Any = 3
    let t = try checkType(Int.self, value: n, name: "n")
    print(t) //->3
} catch let error {
    print(error)
}
do {
    let n: Any = "x"
    let t = try checkType(Int.self, value: n, name: "n")
    print(t)
} catch let error {
    print(error) //->InvalidType("[n] Expected Int, but it was an _NSContiguousString with value: x")
}

希望这对您有效PlaidCategory.init(category:)，但未经测试。

多一个。如果仅在可推断返回类型的地方使用它，则无需传递type参数。

func checkType<T, U>(value: T?, name: String) throws -> U {
    guard let value = value else {
        let message = "[\(name)] Expected \(U.self), but value was nil"
        throw PlaidsterError.InvalidType(message)
    }

    guard let result = value as? U else {
        let message = "[\(name)] Expected \(U.self), but it was an \(value.dynamicType) with value: \(value)"
        throw PlaidsterError.InvalidType(message)
    }

    return result
}

并将其用作：

do {
    let n: Any = "x"
    let t: Int = try checkType(n, name: "n")
    print(t)
} catch let error {
    print(error) //->InvalidType("[n] Expected Int, but it was an String with value: x")
}

或者：

public struct PlaidCategory {

    // MARK: Properties
    public let id: String
    public let hierarchy: [String]
    public let type: String

    // MARK: Initialization
    public init(category: [String: Any]) throws {
        id = try checkType(category["id"], name: "id")
        hierarchy = try checkType(category["hierarchy"], name: "hierarchy")
        type = try checkType(category["type"], name: "type")
    }
}

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