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混合泛型类型的Swift数组

generics swift

Thomas Joulin · 技术社区 · 7 年前

想知道为什么这不可能:

class Test<T, U> {

    init(key: T, value: U) {
    }

}

let array: [Test<String, Any>] = [
    Test<String, Double>(key: "test", value: 42),
    Test<String, Array>(key: "test", value: [])
]

我收到一个错误:

错误:无法将“Test”类型的值转换为预期值元件类型“测试”

更新:遵循Brduca的回答

这是怎么回事:

class Test<T, U> {

    let key: T
    let value: U

    init(key: T, value: U) {
        self.key = key
        self.value = value
    }

}

let properties: [Test<String, Any>] = [
    Test(key: "fontSize", value: []),
    Test(key: "textColor", value: 42)
]

但事实并非如此:

class TestBlock<T, U> {

    let key: String
    let block: (T, U) -> Void

    init(key: String, block: @escaping (T, U) -> Void) {
        self.key = key
        self.block = block
    }

}

let block1: (UILabel, CGFloat) -> Void = {
    $0.font = $0.font.withSize($1)
}

let block2: (UILabel, UIColor) -> Void = {
    $0.textColor = $1
}

let propertiesWithBlock: [TestBlock<UILabel, Any>] = [
    TestBlock(key: "fontSize", block: block1),
    TestBlock(key: "textColor", block: block2)
]

我收到以下错误:

Cannot convert value of type 'TestBlock<UILabel, CGFloat>' to expected element type 'TestBlock<UILabel, Any>'

3 回复 | 直到 7 年前

brduca 7 年前

无需显式键入:

class Test<T, U> {

    init(key: T, value: U) {
    }

}

let array: [Test<String, Any>] = [

    Test(key: "test", value: []),
    Test(key: "test", value: 42)
]

更新时间:

typealias tuple = (Any,Any)

class TestBlock
{
    let key: String
    let block: (tuple) -> Void

    init(key: String, block: @escaping (tuple) -> Void)
    {
        self.key = key
        self.block = block
    }
}

let block1: (tuple) -> Void = { (arg) in

    let (_label, _size) = arg
    let label = _label as! UILabel
    label.font = label.font.withSize((_size as! CGFloat))
}

let block2: (tuple) -> Void = { (arg) in

    let (_label, _color) = arg
    let label = _label as! UILabel
    let color = _color as! UIColor
    label.textColor = color
}

let propertiesWithBlock: [TestBlock] = [

    TestBlock(key: "fontSize", block: block1),
    TestBlock(key: "textColor", block: block2)
]

Renetik 5 年前

我找到了“变通方法”,但没人喜欢。基本上,您可以为测试创建基类,并在从数组访问时将希望调用的任何函数放在基类上。您还可以使其实现Equalable,或创建另一个实现它的可重用类:

class TestBase: CSObject {
   open func someFunction(){ fatalError() }
}

open class CSObject: Equatable {
    public static func ==(lhs: CSObject, rhs: CSObject) -> Bool {
        lhs === rhs
    }
}

//Now make your Test extend TestBase and use that in your Arrays:

class Test<T, U> : TestBase {

    init(key: T, value: U) {
    }

    @override func someFunction(){
       //...do some work that is accessible from array
    }
}

let array: [TestBase] = [
    Test<String, Double>(key: "test", value: 42.0),
    Test<String, Array>(key: "test", value: [])
]

array[0].someFunction() // :)

这对我来说就像一个笑话。。。编写简单的泛型列表已经有好几年了,但swift就是不允许,因为它有无数愚蠢的类型安全限制,使开发更加耗时。

当然,这只是针对某些情况的解决方案。。。

-1

Ahmad F 7 年前

你犯了这个错误,因为 heterogeneous collection literal could only be inferred to '[Any]' 。

这意味着编译器无法解析关系btw Test<String, Double> ,则, Test<String, Array> 和 <String, Any> 类型。

这和你想说的一样 Int 和 String 插入数组,而不将其指定为 [Any] 。

作为您可以使用的解决方案 Brduca's answer 或者可以将数组标记为 [任何]

let array: [Any] = [
    Test<String, Double>(key: "test", value: 42.0),
    Test<String, Array>(key: "test", value: [])
]