Groovy等效于Java 8 ::(双冒号)运算符 [英] Groovy equivalent of Java 8 :: (double colon) operator

问题描述

相当于Java 8 ::(双冒号运算符)在Groovy中?

我正在尝试用groovy翻译此示例 https://github.com/bytefish/PgBulkInsert

但是映射部分的工作方式与Java 8不同:

public PersonBulkInserter() {
    super("sample", "unit_test");

    mapString("first_name", Person::getFirstName);
    mapString("last_name", Person::getLastName);
    mapDate("birth_date", Person::getBirthDate);
}

解决方案

Groovy确实没有实例分离的实例方法引用(还.请参见Wavyx对这个答案的评论.) ，因此您必须使用闭包来伪造它.在Java 8中使用实例方法引用语法时，您实际上是在设置与希望将调用实例作为其第一个(在此例中，仅是)参数的lambda等效的对象.

因此，要在Groovy中获得相同的效果，我们必须创建一个使用默认it参数作为调用实例的闭包.像这样:

PersonBulkInserter() {
    super("sample", "unit_test")

    mapString("first_name", { it.firstName } as Function)
    mapString("last_name", { it.lastName } as Function)
    mapDate("birth_date", { it.birthDate } as Function)
}

请注意此处使用Groovy属性符号，并且必须将Closure强制转换为mapString()或mapDate()方法所期望的@FunctionalInterface类型.

What would the equivalent to Java 8 :: (double colon operator) in Groovy?

I'm trying to translate this example in groovy https://github.com/bytefish/PgBulkInsert

But the mapping part doesn't work the same way as Java 8:

public PersonBulkInserter() {
    super("sample", "unit_test");

    mapString("first_name", Person::getFirstName);
    mapString("last_name", Person::getLastName);
    mapDate("birth_date", Person::getBirthDate);
}

解决方案

Groovy doesn't really have instance-divorced instance-method references (EDIT: Yet. See Wavyx's comment on this answer.), so instead you have to fake it with closures. When using instance-method reference syntax in Java 8, you are really setting up the equivalent of a lambda that expects the invoking instance as its first (in this case, only) argument.

Thus, to get the same effect in Groovy we have to create a closure that uses the default it argument as the invoking instance. Like this:

PersonBulkInserter() {
    super("sample", "unit_test")

    mapString("first_name", { it.firstName } as Function)
    mapString("last_name", { it.lastName } as Function)
    mapDate("birth_date", { it.birthDate } as Function)
}

Notice the use of Groovy property notation here, and that it is necessary to cast the Closure to the @FunctionalInterface type expected by the mapString() or mapDate() method.

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