我怎样才能在斯威夫特扩展类型数组？ [英] How can I extend typed Arrays in Swift?

问题描述

如何延长斯威夫特的阵列＆LT; T＆GT; 或 T [] 自定义功能utils的类型？

How can I extend Swift's Array<T> or T[] type with custom functional utils?

各地斯威夫特的API文档浏览显示，阵列方法是为扩展名的 T [] ，例如：

Browsing around Swift's API docs shows that Array methods are an extension of the T[], e.g:

extension T[] : ArrayType {
    //...
    init()

    var count: Int { get }

    var capacity: Int { get }

    var isEmpty: Bool { get }

    func copy() -> T[]
}

在复制和粘贴相同的源，并试图像任何变化：

When copying and pasting the same source and trying any variations like:

extension T[] : ArrayType {
    func foo(){}
}

extension T[] {
    func foo(){}
}

据构建失败，错误：

It fails to build with the error:

标称型 T [] 不能延长

使用完整的类型定义失败，使用未定义类型'T'的，即：

Using the full type definition fails with Use of undefined type 'T', i.e:

extension Array<T> {
    func foo(){}
}

和它也失败，阵列＆LT; T：。任何＆GT; 和阵列＆LT;弦乐＆GT;

奇怪的是斯威夫特让我带扩展非类型化的数组：

Curiously Swift lets me extend an untyped array with:

extension Array {
    func each(fn: (Any) -> ()) {
        for i in self {
            fn(i)
        }
    }
}

它让我打电话：

[1,2,3].each(println)

但作为类型似乎是失去了当它流经的方法，如争取的更换斯威夫特的内建有过滤器：

extension Array {
    func find<T>(fn: (T) -> Bool) -> T[] {
        var to = T[]()
        for x in self {
            let t = x as T
            if fn(t) {
                to += t
            }
        }
        return to
    }
}

但是，编译器将其视为无类型它仍然允许调用带有扩展名：

But the compiler treats it as untyped where it still allows calling the extension with:

["A","B","C"].find { $0 > "A" }

和加强的时候得来速与调试表示该类型是 Swift.String 但它是一个生成错误尝试像一个字符串访问它，没有它转换为字符串第一，即：

And when stepped-thru with a debugger indicates the type is Swift.String but it's a build error to try access it like a String without casting it to String first, i.e:

["A","B","C"].find { ($0 as String).compare("A") > 0 }

有谁知道什么是创造，它如同内置的扩展类型化扩展方法的正确方法？

Does anyone know what's the proper way to create a typed extension method that acts like the built-in extensions?

推荐答案

一个尝试不同的事情解决后似乎删除＆LT;从喜欢签名; T＆GT

After a while trying different things the solution seems to remove the <T> from the signature like:

extension Array {
    func find(fn: (T) -> Bool) -> [T] {
        var to = [T]()
        for x in self {
            let t = x as T;
            if fn(t) {
                to += t
            }
        }
        return to
    }
}

现在按预期工作不生成错误：

Which now works as intended without build errors:

["A","B","C"].find { $0.compare("A") > 0 }

这篇关于我怎样才能在斯威夫特扩展类型数组？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！