Visitorパターンの2変数以上への拡張

TypesafeBinaryVisitorSample.java

public class TypesafeBinaryVisitorSample {
    public static abstract class Type implements Acceptor {
        private Type(){}

        public static final class Type1 extends Type {
            @Override
            public <R> R accept(Visitor1<R> visitor1) {
                return visitor1.visit(this);
            }
        }
        public static final class Type2 extends Type {
            @Override
            public <R> R accept(Visitor1<R> visitor1) {
                return visitor1.visit(this);
            }
        }
        public static final class Type3 extends Type {
            @Override
            public <R> R accept(Visitor1<R> visitor1) {
                return visitor1.visit(this);
            }
        }
    }

    interface Acceptor {
        <R> R accept(Visitor1<R> visitor1);
    }

    public interface Visitor1<R> {
        default R apply(Type t1) {
            return t1.accept(this);
        }

        R visit(Type.Type1 t1);

        R visit(Type.Type2 t1);

        R visit(Type.Type3 t1);
    }

    public interface Visitor2<R> extends Visitor1<Visitor1<R>> {
        default R apply(Type t1, Type t2) {
            return apply(t1).apply(t2);
        }

        @Override
        default Visitor1<R> visit(Type.Type1 t1) {
            return new Visitor1<>() {
                @Override
                public R visit(Type.Type1 t2) {
                    return Visitor2.this.visit(t1, t2);
                }

                @Override
                public R visit(Type.Type2 t2) {
                    return Visitor2.this.visit(t1, t2);
                }

                @Override
                public R visit(Type.Type3 t2) {
                    return Visitor2.this.visit(t1, t2);
                }
            };
        }

        @Override
        default Visitor1<R> visit(Type.Type2 t1) {
            return new Visitor1<>() {
                @Override
                public R visit(Type.Type1 t2) {
                    return Visitor2.this.visit(t1, t2);
                }

                @Override
                public R visit(Type.Type2 t2) {
                    return Visitor2.this.visit(t1, t2);
                }

                @Override
                public R visit(Type.Type3 t2) {
                    return Visitor2.this.visit(t1, t2);
                }
            };
        }

        @Override
        default Visitor1<R> visit(Type.Type3 t1) {
            return new Visitor1<>() {
                @Override
                public R visit(Type.Type1 t2) {
                    return Visitor2.this.visit(t1, t2);
                }

                @Override
                public R visit(Type.Type2 t2) {
                    return Visitor2.this.visit(t1, t2);
                }

                @Override
                public R visit(Type.Type3 t2) {
                    return Visitor2.this.visit(t1, t2);
                }
            };
        }

        R visit(Type.Type1 t1, Type.Type1 t2);

        R visit(Type.Type1 t1, Type.Type2 t2);

        R visit(Type.Type1 t1, Type.Type3 t2);

        R visit(Type.Type2 t1, Type.Type1 t2);

        R visit(Type.Type2 t1, Type.Type2 t2);

        R visit(Type.Type2 t1, Type.Type3 t2);

        R visit(Type.Type3 t1, Type.Type1 t2);

        R visit(Type.Type3 t1, Type.Type2 t2);

        R visit(Type.Type3 t1, Type.Type3 t2);
    }

    public interface CommutativeVisitor2<R> extends Visitor2<R> {
        @Override
        default R visit(Type.Type2 t1, Type.Type1 t2) {
            return apply(t2, t1);
        }

        @Override
        default R visit(Type.Type3 t1, Type.Type1 t2) {
            return apply(t2, t1);
        }

        @Override
        default R visit(Type.Type3 t1, Type.Type2 t2) {
            return apply(t2, t1);
        }
    }

    public interface Visitor3<R> extends Visitor2<Visitor1<R>> {
        default R apply(Type t1, Type t2, Type t3) {
            return apply(t1, t2).apply(t3);
        }

        @Override
        default Visitor1<R> visit(Type.Type1 t1, Type.Type1 t2) {
            return new Visitor1<>() {
                @Override
                public R visit(Type.Type1 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }

                @Override
                public R visit(Type.Type2 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }

                @Override
                public R visit(Type.Type3 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }
            };
        }

        @Override
        default Visitor1<R> visit(Type.Type1 t1, Type.Type2 t2) {
            return new Visitor1<>() {
                @Override
                public R visit(Type.Type1 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }

                @Override
                public R visit(Type.Type2 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }

                @Override
                public R visit(Type.Type3 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }
            };
        }

        @Override
        default Visitor1<R> visit(Type.Type1 t1, Type.Type3 t2) {
            return new Visitor1<>() {
                @Override
                public R visit(Type.Type1 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }

                @Override
                public R visit(Type.Type2 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }

                @Override
                public R visit(Type.Type3 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }
            };
        }

        @Override
        default Visitor1<R> visit(Type.Type2 t1, Type.Type1 t2) {
            return new Visitor1<>() {
                @Override
                public R visit(Type.Type1 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }

                @Override
                public R visit(Type.Type2 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }

                @Override
                public R visit(Type.Type3 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }
            };
        }

        @Override
        default Visitor1<R> visit(Type.Type2 t1, Type.Type2 t2) {
            return new Visitor1<>() {
                @Override
                public R visit(Type.Type1 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }

                @Override
                public R visit(Type.Type2 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }

                @Override
                public R visit(Type.Type3 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }
            };
        }

        @Override
        default Visitor1<R> visit(Type.Type2 t1, Type.Type3 t2) {
            return new Visitor1<>() {
                @Override
                public R visit(Type.Type1 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }

                @Override
                public R visit(Type.Type2 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }

                @Override
                public R visit(Type.Type3 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }
            };
        }

        @Override
        default Visitor1<R> visit(Type.Type3 t1, Type.Type1 t2) {
            return new Visitor1<>() {
                @Override
                public R visit(Type.Type1 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }

                @Override
                public R visit(Type.Type2 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }

                @Override
                public R visit(Type.Type3 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }
            };
        }

        @Override
        default Visitor1<R> visit(Type.Type3 t1, Type.Type2 t2) {
            return new Visitor1<>() {
                @Override
                public R visit(Type.Type1 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }

                @Override
                public R visit(Type.Type2 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }

                @Override
                public R visit(Type.Type3 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }
            };
        }

        @Override
        default Visitor1<R> visit(Type.Type3 t1, Type.Type3 t2) {
            return new Visitor1<>() {
                @Override
                public R visit(Type.Type1 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }

                @Override
                public R visit(Type.Type2 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }

                @Override
                public R visit(Type.Type3 t3) {
                    return Visitor3.this.visit(t1, t2, t3);
                }
            };
        }

        R visit(Type.Type1 t1, Type.Type1 t2, Type.Type1 t3);

        R visit(Type.Type1 t1, Type.Type1 t2, Type.Type2 t3);

        R visit(Type.Type1 t1, Type.Type1 t2, Type.Type3 t3);

        R visit(Type.Type1 t1, Type.Type2 t2, Type.Type1 t3);

        R visit(Type.Type1 t1, Type.Type2 t2, Type.Type2 t3);

        R visit(Type.Type1 t1, Type.Type2 t2, Type.Type3 t3);

        R visit(Type.Type1 t1, Type.Type3 t2, Type.Type1 t3);

        R visit(Type.Type1 t1, Type.Type3 t2, Type.Type2 t3);

        R visit(Type.Type1 t1, Type.Type3 t2, Type.Type3 t3);

        R visit(Type.Type2 t1, Type.Type1 t2, Type.Type1 t3);

        R visit(Type.Type2 t1, Type.Type1 t2, Type.Type2 t3);

        R visit(Type.Type2 t1, Type.Type1 t2, Type.Type3 t3);

        R visit(Type.Type2 t1, Type.Type2 t2, Type.Type1 t3);

        R visit(Type.Type2 t1, Type.Type2 t2, Type.Type2 t3);

        R visit(Type.Type2 t1, Type.Type2 t2, Type.Type3 t3);

        R visit(Type.Type2 t1, Type.Type3 t2, Type.Type1 t3);

        R visit(Type.Type2 t1, Type.Type3 t2, Type.Type2 t3);

        R visit(Type.Type2 t1, Type.Type3 t2, Type.Type3 t3);

        R visit(Type.Type3 t1, Type.Type1 t2, Type.Type1 t3);

        R visit(Type.Type3 t1, Type.Type1 t2, Type.Type2 t3);

        R visit(Type.Type3 t1, Type.Type1 t2, Type.Type3 t3);

        R visit(Type.Type3 t1, Type.Type2 t2, Type.Type1 t3);

        R visit(Type.Type3 t1, Type.Type2 t2, Type.Type2 t3);

        R visit(Type.Type3 t1, Type.Type2 t2, Type.Type3 t3);

        R visit(Type.Type3 t1, Type.Type3 t2, Type.Type1 t3);

        R visit(Type.Type3 t1, Type.Type3 t2, Type.Type2 t3);

        R visit(Type.Type3 t1, Type.Type3 t2, Type.Type3 t3);
    }

    public static final class Cat implements Visitor2<String> {
        public String visit(Type.Type1 t1, Type.Type1 t2) {
            return "Type1-Type1";
        }

        public String visit(Type.Type1 t1, Type.Type2 t2) {
            return "Type1-Type2";
        }

        public String visit(Type.Type1 t1, Type.Type3 t2) {
            return "Type1-Type3";
        }

        public String visit(Type.Type2 t1, Type.Type1 t2) {
            return "Type2-Type1";
        }

        public String visit(Type.Type2 t1, Type.Type2 t2) {
            return "Type2-Type2";
        }

        public String visit(Type.Type2 t1, Type.Type3 t2) {
            return "Type2-Type3";
        }

        public String visit(Type.Type3 t1, Type.Type1 t2) {
            return "Type3-Type1";
        }

        public String visit(Type.Type3 t1, Type.Type2 t2) {
            return "Type3-Type2";
        }

        public String visit(Type.Type3 t1, Type.Type3 t2) {
            return "Type3-Type3";
        }
    }

    public static final class Sum implements CommutativeVisitor2<Integer> {
        @Override
        public Integer visit(Type.Type1 t1, Type.Type1 t2) {
            return 2;
        }

        @Override
        public Integer visit(Type.Type1 t1, Type.Type2 t2) {
            return 3;
        }

        @Override
        public Integer visit(Type.Type1 t1, Type.Type3 t2) {
            return 4;
        }

        @Override
        public Integer visit(Type.Type2 t1, Type.Type2 t2) {
            return 4;
        }

        @Override
        public Integer visit(Type.Type2 t1, Type.Type3 t2) {
            return 5;
        }

        @Override
        public Integer visit(Type.Type3 t1, Type.Type3 t2) {
            return 6;
        }
    }

    public static final class ToString implements Visitor1<String> {
        @Override
        public String visit(Type.Type1 t1) {
            return "Type1";
        }

        @Override
        public String visit(Type.Type2 t1) {
            return "Type2";
        }

        @Override
        public String visit(Type.Type3 t1) {
            return "Type3";
        }
    }

    public static final class Cat3 implements Visitor3<String> {

        @Override
        public String visit(Type.Type1 t1, Type.Type1 t2, Type.Type1 t3) {
            return "Type1-Type1-Type1";
        }

        @Override
        public String visit(Type.Type1 t1, Type.Type1 t2, Type.Type2 t3) {
            return "Type1-Type1-Type2";
        }

        @Override
        public String visit(Type.Type1 t1, Type.Type1 t2, Type.Type3 t3) {
            return "Type1-Type1-Type3";
        }

        @Override
        public String visit(Type.Type1 t1, Type.Type2 t2, Type.Type1 t3) {
            return "Type1-Type2-Type1";
        }

        @Override
        public String visit(Type.Type1 t1, Type.Type2 t2, Type.Type2 t3) {
            return "Type1-Type2-Type2";
        }

        @Override
        public String visit(Type.Type1 t1, Type.Type2 t2, Type.Type3 t3) {
            return "Type1-Type2-Type3";
        }

        @Override
        public String visit(Type.Type1 t1, Type.Type3 t2, Type.Type1 t3) {
            return "Type1-Type3-Type1";
        }

        @Override
        public String visit(Type.Type1 t1, Type.Type3 t2, Type.Type2 t3) {
            return "Type1-Type3-Type2";
        }

        @Override
        public String visit(Type.Type1 t1, Type.Type3 t2, Type.Type3 t3) {
            return "Type1-Type3-Type3";
        }

        @Override
        public String visit(Type.Type2 t1, Type.Type1 t2, Type.Type1 t3) {
            return "Type2-Type1-Type1";
        }

        @Override
        public String visit(Type.Type2 t1, Type.Type1 t2, Type.Type2 t3) {
            return "Type2-Type1-Type2";
        }

        @Override
        public String visit(Type.Type2 t1, Type.Type1 t2, Type.Type3 t3) {
            return "Type2-Type1-Type3";
        }

        @Override
        public String visit(Type.Type2 t1, Type.Type2 t2, Type.Type1 t3) {
            return "Type2-Type2-Type1";
        }

        @Override
        public String visit(Type.Type2 t1, Type.Type2 t2, Type.Type2 t3) {
            return "Type2-Type2-Type2";
        }

        @Override
        public String visit(Type.Type2 t1, Type.Type2 t2, Type.Type3 t3) {
            return "Type2-Type2-Type3";
        }

        @Override
        public String visit(Type.Type2 t1, Type.Type3 t2, Type.Type1 t3) {
            return "Type2-Type3-Type1";
        }

        @Override
        public String visit(Type.Type2 t1, Type.Type3 t2, Type.Type2 t3) {
            return "Type2-Type3-Type2";
        }

        @Override
        public String visit(Type.Type2 t1, Type.Type3 t2, Type.Type3 t3) {
            return "Type2-Type3-Type3";
        }

        @Override
        public String visit(Type.Type3 t1, Type.Type1 t2, Type.Type1 t3) {
            return "Type3-Type1-Type1";
        }

        @Override
        public String visit(Type.Type3 t1, Type.Type1 t2, Type.Type2 t3) {
            return "Type3-Type1-Type2";
        }

        @Override
        public String visit(Type.Type3 t1, Type.Type1 t2, Type.Type3 t3) {
            return "Type3-Type1-Type3";
        }

        @Override
        public String visit(Type.Type3 t1, Type.Type2 t2, Type.Type1 t3) {
            return "Type3-Type2-Type1";
        }

        @Override
        public String visit(Type.Type3 t1, Type.Type2 t2, Type.Type2 t3) {
            return "Type3-Type2-Type2";
        }

        @Override
        public String visit(Type.Type3 t1, Type.Type2 t2, Type.Type3 t3) {
            return "Type3-Type2-Type3";
        }

        @Override
        public String visit(Type.Type3 t1, Type.Type3 t2, Type.Type1 t3) {
            return "Type3-Type3-Type1";
        }

        @Override
        public String visit(Type.Type3 t1, Type.Type3 t2, Type.Type2 t3) {
            return "Type3-Type3-Type2";
        }

        @Override
        public String visit(Type.Type3 t1, Type.Type3 t2, Type.Type3 t3) {
            return "Type3-Type3-Type3";
        }
    }

    public static void main(String[] args) {
        Type unknownType1 = new Type.Type1();
        Type unknownType2 = new Type.Type2();
        Type unknownType3 = new Type.Type1();

        var cat = new Cat();
        System.out.println(cat.apply(unknownType1, unknownType2));
        System.out.println(cat.apply(unknownType2, unknownType1));

        var sum = new Sum();
        System.out.println(sum.apply(unknownType1, unknownType2));
        System.out.println(sum.apply(unknownType2,unknownType1));

        var toString = new ToString();
        System.out.println(toString.apply(unknownType1));
        System.out.println(toString.apply(unknownType2));

        var cat3 = new Cat3();
        System.out.println(cat3.apply(unknownType1, unknownType2, unknownType3));
    }
}