Question

我想创建一个执行某些处理的通用辅助函数。其中一个输入将是一个返回一组数据的函数。

我无法弄清楚如何做到这一点。我一直收到编译错误。我找到了帖子

argument for generic parameter could not be inferred

并尝试添加...as [String]或... as [Int]等，但没有运气。

func helperThatDoesSomeGenericProcessing<T>(displayedStrings: () -> [T])  -> [String]! {
    let listOfSomething: [T] = displayedStrings()
    // do something with listOfSomething
    return ["some", "resulting", "string", "from", "the", "input"]
}

func concreteFunction1() -> [AnyObject]! {
    var s: [String] = helperThatDoesSomeGenericProcessing {  // ERROR: Argument for generic parameter 'T' could not be inferred.
        var str = ["One", "Two", "Three"]
    } // tried 'as [String]' here

    // do something with s
    return s
}

func concreteFunction2() -> [AnyObject]! {
    var s: [Int] = helperThatDoesSomeGenericProcessing {  // ERROR: Argument for generic parameter 'T' could not be inferred.
        var i = [1, 2, 3]
    } // tried 'as [Int]' here

    // do something with s
    return s
}

Answer 1

正确地添加return并明确声明() -> [T]的具体类型可以解决错误......但我不确定它能为您提供所需内容。无论如何，这里是代码：

func helperThatDoesSomeGenericProcessing<T>(displayedStrings: () -> [T])  -> [String]! {
    let listOfSomething: [T] = displayedStrings()
    // do something with listOfSomething
    return ["some", "resulting", "string", "from", "the", "input"]
}

func concreteFunction1() -> [AnyObject]! {
    var s: [String]! = helperThatDoesSomeGenericProcessing {
        () -> [String] in // Explicit declared type
        var str = ["One", "Two", "Three"]
        return str
    } // tried 'as [String]' here

    // do something with s
    return s
}

func concreteFunction2() -> [AnyObject]! {
    var s: [String]! = helperThatDoesSomeGenericProcessing {
        () -> [Int] in // Explicit declared type
        var i = [1, 2, 3]
        return i
    } // tried 'as [Int]' here

    // do something with s
    return s
}

注意我还更正了var s的类型，因为你的泛型函数总是返回一个隐式解包的可选字符串数组[String]!。返回类型不是一般化的（即：T或[T]等）。

可能您可能需要更改某些类型声明以满足您的设计需求。

希望这有帮助

Answer 2

你的封闭体不会返回

func concreteFunction1() -> [AnyObject]! {
    let s: [String] = helperThatDoesSomeGenericProcessing {  // ERROR: Argument for generic parameter 'T' could not be inferred.
    return ["One", "Two", "Three"]
} // tried 'as [String]' here

    // do something with s
    return s
}

通用参数的参数＆＃39; T＆＃39;无法推断

2 个答案: