适当的教堂所有权领域

Question

在 init 中创建的对象字段的适当所有权是什么？我认为最好使用 "owned"，但看起来它在 init 完成后不会保留那些。

运行这个代码... (Try it online!)

class Name {

    var text : string;

    //initializer
    proc init(name : string) {
        this.text = name;
    }

        proc writeThis(writer) {
        writer.writeln(this.text);
    }   
} //end of Name

class Monkey {

        var name : Name;
        var age : int;

        proc init(name : string, age : int) {
            this.name = new owned Name(name);
            this.age = age;
        }

    proc writeThis(writer) {
        writer.writeln("I'm a monkey named ", this.name, ", and I'm ", this.age, " years old.");
    }

} //end of class Monkey



var m = new owned Monkey("bananaface", 5);
writeln("m: ", m);

... 使其仅打印：

m: I'm a monkey named

Try it online!

在 Monkey 的 init 中，有什么比设置 this.name = new owned Name(...) 更合适的所有权？

Answer 1

我用预发布的 1.19 版本（即将发布）试用了你的程序，它打印出来了

monkeys.chpl:20: In initializer:
monkeys.chpl:21: error: Field name would outlive the value it is set to

下面我来说明问题：

class Name { ... }
class Monkey {
  var name : Name;
  proc init(name : string) {
    this.name = new owned Name(name);
  }
}

相当于

class Name { ... }
class Monkey {
  var name : borrowed Name;
  proc init(name : string) {
    this.name = new owned Name(name);
  }
}

与

相同

class Name { ... }
class Monkey {
  var name : borrowed Name;
  proc init(name : string) {
    var tmp = new owned Name(name);
    this.name = tmp.borrow();
    // the instance in tmp is automatically deleted here
  }
}

你也许可以更清楚地看到 new owned 的结果在初始化程序结束时被销毁了。

修复很简单：将字段声明为 var name: owned Name;:

class Name { ... }
class Monkey {
  var name : owned Name;
  proc init(name : string) {
    this.name = new owned Name(name);
  }
}

适当的教堂所有权领域

Appropriate chapel ownership for fields

chapel