锡兰元模型

Question

我正在研究 Ceylon 并且对它的元模型有疑问。我想创建一些 create some base class 'DataContainer' 允许实例化不可变 classes 与内置 equals-hash 实现：例如标识符（125，"ab"）==标识符（125，"ab"）所以 base class 应该收集所有共享的非变量值并在 'hash' 和 'equals' 方法中使用这些信息。我写了这段代码：

shared abstract class DataContainer(ClassDeclaration declaration) {
    value members = {
        for (i in declaration.memberDeclarations<ValueDeclaration>())
            if (!i.variable, i.name != "hash", i.name != "string") i
    };
    variable Integer? hashCode = null;

    shared actual Boolean equals(Object that) {
        if (is DataContainer that) {
            for (item in members) {
                value thisMember = item.memberGet(this);
                value thatMember = item.memberGet(that);
                if (exists thisMember, exists thatMember) {
                    if (thisMember != thatMember) { return false; }
                } else if (thisMember exists != thatMember exists) { return false; }
            }
            return true;
        }
        return false;
    }

    shared actual Integer hash => hashCode else (hashCode = calculateHash());

    Integer calculateHash() {
        variable value result = 0;
        for(i in members) {
            if (exists member = i.memberGet(this)) {
                result = result.xor(member.hash);
            }
        }
        return result;
    }
}

class Identifier(shared Integer? id, shared String? name) extends DataContainer(`class`) {}

标识符class是DataContainer的客户端。我总体上喜欢这个解决方案，但我必须将 'class' 传递给超级 class 构造函数，因为如果我在 DataContainer 中使用 'class' 它看不到 subclass 的任何成员. 如何在基本 class 方法中获取扩展 class 成员的实际列表？ 'this' 之类的东西不起作用...

Answer 1

感谢 Ceylon 社区的人，我找到了解决方案。应该使用 ceylon.language.meta 中的函数 classDeclaration(this) 而不是 'class'.

这是最终代码：

shared abstract class DataContainer() {
    variable Integer? _hash = null;
    variable ValueDeclaration[]? _members = null;

    shared actual Boolean equals(Object that) {
        if (is DataContainer that) {
            for (i in members) {
                value thisMember = i.memberGet(this);
                value thatMember = i.memberGet(that);
                if (exists thisMember, exists thatMember) {
                    if (thisMember != thatMember) { return false; }
                } else if (thisMember exists != thatMember exists) { return false; }
            }
            return true;
        }
        return false;
    }

    shared actual Integer hash => _hash else (_hash = calculateHash());

    ValueDeclaration[] members => _members else (_members = [
        for (i in classDeclaration(this).memberDeclarations<ValueDeclaration>())
            if (!i.variable, i.name != "string", i.name != "hash") i
    ]);

    Integer calculateHash() {
        variable Integer result = 0;
        for (i in members) {
            if (exists member = i.memberGet(this)) {
                result = result.xor(member.hash);
            }
        }
        return result;
    }
}

class Identifier(shared Integer? number, shared String? name) extends DataContainer() {}

Answer 2

除了 Alexander 令人生畏的回答之外，我还冒昧地实现了一个 string 函数，这样您就可以 print(myObj) 并且它呈现得很好：

shared default actual String string {
    value s = StringBuilder();
    s.append(type(this).declaration.name).append(" { ");
    for (i in members) {
        value m = i.memberGet(this);
        s.append(i.name).append(":");
        s.append(if(exists m) then m.string else "<null>");
    }
    return s.append(" }").string;
}

锡兰元模型

Ceylon metamodel

reflection

metamodel

ceylon