相当于 Java 8 ::(双冒号)运算符的 Groovy [英] Groovy equivalent of Java 8 :: (double colon) operator

问题描述

Java 8 的等价物是什么 :: (双冒号运算符) 在 Groovy 中?

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

我正在尝试在 groovy https://github.com/bytefish/PgBulkInsert

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

但是映射部分的工作方式与 Java 8 不同:

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);
}

推荐答案

Groovy 并没有真正的实例分离实例方法引用(Yet.请参阅 Wavyx 对此答案的评论.)，所以你必须用闭包来伪造它.在 Java 8 中使用实例方法引用语法时，您实际上是在设置 lambda 的等效项，它期望调用实例作为其第一个(在本例中，仅是)参数.

Groovy doesn't really have instance-divorced instance-method references ( 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.

因此，为了在 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:

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)
}

注意这里使用了 Groovy 属性符号，并且有必要将 Closure 强制转换为 mapString()<所期望的 @FunctionalInterface 类型/code> 或 mapDate() 方法.

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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