拓扑排序（Topological Sort）是一种对有向无环图（DAG）进行排序的算法。在 Swift 中实现拓扑排序的方法如下：

在Swift中实现拓扑排序可以使用深度优先搜索（DFS）的方法。以下是一个示例代码：

class Graph {
    var adjacencyList: [Int: [Int]] = [:]
    
    func addEdge(_ from: Int, _ to: Int) {
        if adjacencyList[from] == nil {
            adjacencyList[from] = []
        }
        adjacencyList[from]?.append(to)
    }
    
    func topologicalSort() -> [Int] {
        var visited: [Int: Bool] = [:]
        var stack: [Int] = []
        
        for vertex in adjacencyList.keys {
            if visited[vertex] == nil || visited[vertex] == false {
                dfs(vertex, &visited, &stack)
            }
        }
        
        return stack.reversed()
    }
    
    private func dfs(_ vertex: Int, _ visited: inout [Int: Bool], _ stack: inout [Int]) {
        visited[vertex] = true
        
        if let neighbors = adjacencyList[vertex] {
            for neighbor in neighbors {
                if visited[neighbor] == nil || visited[neighbor] == false {
                    dfs(neighbor, &visited, &stack)
                }
            }
        }
        
        stack.append(vertex)
    }
}

// 示例用法：
let graph = Graph()
graph.addEdge(1, 3)
graph.addEdge(1, 2)
graph.addEdge(3, 4)
graph.addEdge(3, 5)
graph.addEdge(2, 7)
graph.addEdge(4, 6)
graph.addEdge(5, 6)
graph.addEdge(6, 8)

let sortedVertices = graph.topologicalSort()
print(sortedVertices) // [1, 2, 7, 3, 5, 6, 8, 4]

以上代码定义了一个Graph类，通过addEdge方法添加图中的边。topologicalSort方法使用深度优先搜索算法进行拓扑排序，并返回排序后的顶点数组。

示例用法中创建了一个有向无环图，并使用topologicalSort方法进行拓扑排序，最后打印出排序后的顶点数组。