模式匹配
常用import
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| import static io.vavr.API.$;
import static io.vavr.API.Case;
import static io.vavr.API.Match;
import static io.vavr.Patterns.$Tuple2;
|
简单匹配
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| var name = 1;
String greetMsg = Match(name).of(
Case($(1), "yes"),
Case($(), "no")
);
assertEquals("yes", greetMsg);
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匹配Tuple
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| var t = Tuple.of(1, "joy");
String greetMsg = Match(t).of(
Case($Tuple2($(1), $()), (a, b) -> "hello " + b),
Case($(e -> e._1 == 1), "123"),
Case($(), "unknown")
);
assertEquals("hello joy", greetMsg);
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匹配Try
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| import static io.vavr.API.Try;
import static io.vavr.Patterns.$Failure;
import static io.vavr.Patterns.$Success;
var s = Try(() -> 1);
String r = Match(s).of(
Case($Success($()), "success"),
Case($Failure($()), "failure"),
Case($(), "failure")
);
assertEquals("success", r);
var f = Try(() -> 1 / 0);
String r2 = Match(f).of(
Case($Success($()), "success"),
Case($Failure($(e -> RuntimeException.class.isAssignableFrom(e.getClass()))), "runtime exception"),
Case($Failure($()), "failure"),
Case($(), "unknown")
);
assertEquals("runtime exception", r2);
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对自定义类型进行匹配
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| var p = new Person(1, "joy");
String greetMsg = Match(p).of(
Case(Person.$id(1), (id, name) -> "hello " + name),
Case($(), () -> "unknown")
);
assertEquals("hello joy", greetMsg);
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其中Person如下
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| @AllArgsConstructor
public static class Person {
Integer id;
String name;
public static Match.Pattern2<Person, Integer, String> $id(Integer id) {
return Match.Pattern2.of(Person.class, $(id), $(), _p -> Tuple.of(_p.id, _p.name));
}
}
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一点优化
match的of参数每次需创建n个Case，可使用Supplier优化效率，如下代码
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| @SafeVarargs
public static <T, R> R match(T value, Supplier<Match.Case<? extends T, ? extends R>> ...cases) {
Objects.requireNonNull(cases, "cases is null");
for (var _case : cases) {
@SuppressWarnings("unchecked")
var __case = (Match.Case<T, R>) _case.get();
if (__case.isDefinedAt(value)) {
return __case.apply(value);
}
}
throw new IllegalStateException();
}
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使用方式，增加() ->即可，一个小优化
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| var p = new Person(1, "joy");
String greetMsg = match(p,
() -> Case(Person.$id(1), (id, name) -> "hello " + name),
() -> Case($(), "unknown")
);
assertEquals("hello joy", greetMsg);
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Either
left代表失败，right代表成功
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| Object success = Either.right("value")
.right()
.getOrElse("defaultValue");
assertEquals("value", success);
Object fail = Either.left("error")
.right()
.getOrElse("defaultValue");
assertEquals("defaultValue", fail);
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