arrays - 在两个对象数组之间过滤，避免嵌套 for 循环

Question

在 Swift 4 中，如何将仅检查一个属性是否相等的嵌套 for 循环转换为过滤器？

基本示例:

// Basic object
struct Message {
    let id: String
    let content: String

    init(id: String, content: String) {
        self.id = id
        self.content = content
    }
}

// Array of objects
let local = [Message.init(id: "1234", content: "test1"), Message.init(id: "2345", content: "test2")]

// Array of objects, one has updated content
let server = [Message.init(id: "1234", content: "testDiff1"), Message.init(id: "3456", content: "test3")]

var foundList = [Message]()

// Nested loop to find based on one property matching
for i in local {
    for j in server {
        if i.id == j.id {
            foundList.append(i)
        }
    }
}

这按预期工作(foundList 包含 local[0])，但感觉应该有一种“更快速”的方法来做到这一点？

Answer 1

for 循环可以用一个 for 循环 + where 条件重写:

for m in local where server.contains(where: { $0.id == m.id }) {
    foundList.append(m)
}

或将 filter 与 contains 组合:

foundList = local.filter { m in server.contains(where: { $0.id == m.id }) }

附言此外，使 Message 结构符合 Equatable协议(protocol)。它允许您简化 contains 方法:

for m in local where server.contains(m) {
    foundList.append(m)
}

使用过滤器:

foundList = local.filter { server.contains($0) }