在Kotlin中,HashSet包含按hash重复的元素

val done = HashSet<StudentProgrammeState>()

处理结束时,检查如下:

if (done.distinctBy { it.hashCode() }.size < done.size ) {
    println("Duplicate states were evaluated.")
}

每次运行都会显示此消息。自从 done 是一个 HashSet HashCode

下面是 StudentProgrammeState :

class StudentProgrammeState(val program: Program) {
    val instances = HashSet<StudentModuleInstance>()

    override fun equals(other: Any?): Boolean {
        if (!(other is StudentProgrammeState)) return false
        return (other.program == program) && 
          (other.instances.containsAll(instances) && 
          instances.containsAll(other.instances))
    }
    override fun hashCode() = Objects.hash(program, instances)

Equals 这里不直接检查 hashCode instances 但是这个测试应该对应于无序的集合相等。

对于学生模块仪器:

typealias StudentModuleInstance = Pair<Module, Int>

Pair<> 是内在的 data class equals 和 hashcode

价值 program