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ビルダー

ビルダーを使用すると、ユーザーはより便利な方法でオブジェクトとオブジェクト階層を構成できます。階層内の各オブジェクトを手動でインスタンス化してそのプロパティを 1 つずつ設定する代わりに、専用のビルダーを使用して、より簡潔で直感的な方法で同じデータ構造を作成できます。

例として、家を建てているとしましょう。

House h = new House();
h.houseType = HouseType.detached;
Address address = new Address();
address.street = "Na Lysinach";
address.number = "10";
address.city = "Prague";
address.zipCode = "23459";
h.locate(address);
list<Room> rooms = new arraylist<Room>(0);
rooms.add(new Room("livingroom", 25));
rooms.add(new Room("kitchen", 18));
rooms.add(new Room("bedroom", 20));
rooms.add(new Room("hall", 12));
rooms.add(new Room("bedroom", 15));
h.rooms = rooms;
h.moveIn(6);
println(h);

家には住所が必要です。住所自体はいくつかの項目で構成されており、その中にたくさんの部屋があり、それぞれに 2 つのプロパティが必要です。

面倒な方法の代わりに、ビルダーはあなたに取るべき構文上の近道を与えます:undefined

 House house = new house {
  inhabitants : 6;
  type : HouseType.detached;
  address {
    street : "Na Lysinach";
    number : "10";
    city : "Prague";
    zipCode : "23459";
  }
  room {
    name : "livingroom";
    size : 25;
  }
  room {
    name : "kitchen";
    size : 18;
  }
  room {
    name : "bedroom";
    size : 20;
  }
  room {
    name : "hall";
    size : 12;
  }
  room("bedroom", 15)
};

コードの構造自体は作成されたオブジェクト間の依存関係を反映しているため、コードを見ると、作成されたオブジェクトグラフの構造を素早く把握できます。ビルダーは互いに入れ子になっており、プロパティを保持できます。プロパティ値とビルダーの相互ネストの両方が、その背後に構築されたオブジェクト階層に変換されます。

MPS は、いくつかの言語 - JavaBeans、XML、XMLSchema、または XMLQuery が最も有名なユーザー - の一部として、便利なビルダーを直接あなたの玄関に導きます。

ビルビルダー

To build your own builder, you first need to invoke New -> j.m.baseLanguage.builders.SimpleBuilders. Now you define builders for each object type that participates in the hierarchy. These builders hold their own properties and children, out of which they build the requested data structure. To stick to our earlier "House building" example, check out the sample below:

builders houseBuilders extends <no extendsBuilder> {
  root builder house() extends <no extends> {
    type: House
    create: new House()

    child address {
      attach parent.locate(child);
    }
    child room {
      attach parent.rooms.add(child);
    }
    property inhabitants : int {
      set parent.moveIn(value);
    }
    property type : HouseType {
      set parent.houseType = value;
    }
  }

  builder address() extends <no extends> {
    type: Address
    create: new Address()

    <<children>>
    property street : string {
      set parent.street = value;
    }
    property number : string {
      set parent.number = value;
    }
    property city : string {
      set parent.city = value;
    }
    property zipCode : string {
      set parent.zipCode = value;
    }
  }

  builder room() extends <no extends> {
    type: Room
    create: new Room()

    <<children>>
    property name : string {
      set parent.name = value;
    }
    property size : int {
      set parent.size = value;
    }
  }
 
  builder room(string name, int size) extends <no extends> {
    type: Room
    create: new Room(name, size)

    <<children>>
    <<properties>>
  }
}

We defined a builder for the Room class as well as for the Address class and also a root builder for the House class. Root builders, unlike plain builders, can be used directly in user code after the new keyword. Notice also that we have two builders for the Room class. The first definition allows properties to be nested inside the room block, while the second allows the two properties to come directly as parameters to the room method call. Both approaches can certainly be combined in a single builder.

The House, Room and Address classes in our case are ordinary classes with methods and properties. The methods as well as setters for the properties manipulated in builders must be visible to the builders. The "package" visibility will do in typical cases. To give you an example, see below the House class definition from our example.

 
public class House extends <none> implements <none> {
  <<static fields>>

  <<static initializer>>
  private Address address;
  private int numberOFPeople;
  public HouseType houseType {get; <no visibility> set;}
  public list<Room> rooms {get; <no visibility> set;}
  <<initializer>>

  public House() {
    <no statements>
  }

  public void moveIn(int people) {
    this.numberOFPeople = people;
  }

  public void locate(Address address) {
    this.address = address;
  }

  public int numberOfInhabitants() {
    return this.numberOFPeople;
  }

  public String toString() {
    return "House for " + numberOFPeople + " people at " + address.?toString();
  }

  <<static methods>>

  <<nested classifiers>>
}

最終更新日: 2021 年 2 月 26 日

MPS 2020.3 ヘルプ

ビルダー

ビルビルダー

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