在Swift中使用value objects

最新推荐文章于 2025-08-18 18:20:44 发布

转载最新推荐文章于 2025-08-18 18:20:44 发布 · 150 阅读

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原文链接：https://juejin.im/post/5ce7a7556fb9a07eb55f36fd

文章标签：

#swift

博客围绕Swift中验证用户名的代码展开，指出原代码需在各处调用验证函数的缺点。介绍了值对象概念，其创建时自带验证，拿到即已通过验证。还提及参考系统的设计，具有安全、扩展性强的好处，同时提到contains与allSatisfy的区别。

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验证用户名的代码

func authenticate(user: String) {
    // make sure usernames are at least three characters
    guard user.trimmingCharacters(in: .whitespacesAndNewlines).count >= 3 else {
        print("Username \(user) is too short.")
        return
    }

    // make sure usernames contain no invalid characters
    let illegalCharacters = ["@", "-", "&", "."]
    guard illegalCharacters.contains(where: user.contains) == false else {
        print("Username \(user) contains illegal characters.")
        return
    }

    // Proceed with authentication…
}
``` swift
上面代码的缺点：在其他地方使用会重复

``` swift
extension String {
    func isValidUsername() -> Bool {
        guard self.trimmingCharacters(in: .whitespacesAndNewlines).count >= 3 else {
            return false
        }

        let illegalCharacters = ["@", "-", "&", "."]
        guard illegalCharacters.contains(where: self.contains) == false else {
            return false
        }

        return true
    }
}
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上面代码的缺点：需要在每个地方调用isValidUsername()

struct User: Equatable {
    let value: String

    init?(string: String) {
        guard string.trimmingCharacters(in: .whitespacesAndNewlines).count >= 3 else {
            return nil
        }

        let illegalCharacters = ["@", "-", "&", "."]
        guard illegalCharacters.contains(where: string.contains) == false else {
            return nil
        }

        self.value = string
    }
}

func authenticate(user: User) {
    // Proceed with authentication…
}

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值对象：value objects should be both immutable and equatable, but they also add in validation as part of their creation. This means that if you’re handed a value object you know for sure it’s already passed validation – you don’t need to re-validate it, because if it were valid then it couldn’t exist.

设计：参考系统的 URL(string: "This ain't it chief") 好处：安全，扩展性强

注：contains与allSatisfy的区别

// 有一个满足就为true
func contains(where predicate: (Element) throws -> Bool) rethrows -> Bool
// 所以满足就为true
func allSatisfy(_ predicate: (Element) throws -> Bool) rethrows -> Bool
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