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我正在研究锡兰并对它的元模型有疑问。我想创建一些创建一些基类'DataContainer'，它允许使用内置的equals-hash实现实例化不可变类：例如Identifier（125，“ab”）== Identifier（125，“ab”）所以基类应该收集所有共享的非变量值，并在“哈希”和“等于”方法中使用此信息。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`) {}

Identifier 类是 DataContainer 的客户端。我整体上喜欢这个解决方案，但我必须将“类”传递给超类构造函数，因为如果我在 DataContainer 中使用“类”，它就看不到任何子类的成员。如何在基类方法中获取扩展类成员的实际列表？像'this'这样的东西不起作用......

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2 回答 2

2

感谢锡兰社区的人，我找到了解决方案。应该使用来自 ceylon.language.meta 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() {}
于 2017-12-01T16:18:01.397 回答
0

Adding to Alexander's formidable answer, I took the liberty to implement a string function as well so you can just print(myObj) and it renders nicely:

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;
}
于 2018-09-13T05:04:30.613 回答