     private init() {}
 
     // TODO: Set vs Array (performance) ?
+    // TODO: 看吧，到底用不用遍历全部约束？甚至从来没有一个 Dependency.hasSet -> false 的情况发生！
     /// 全部约束
     var dependencies = Set<Dependency>()
 

    var dependencyHolder: Dependency?

    /// 未设定约束相关信息
    var unsetDependencyInfo : (has: Bool, unsetDependencies: [Dependency]) {
        let unsetDeps = dependencies.filter { dep in
            !dep.hasSet
        }

        return true
    }

    func setDependenciesOf(view: UIView) {

        // 抽取所有需要设定的约束
        let _dependenciesShowP = dependencies.filter { dependency in
