泛型 – 泛型类型的闭包参数 – 异常

在下面的代码中,为什么Groovy似乎忽略了方法barMany中提供的closure参数的泛型类型声明：

import groovy.transform.CompileStatic

@CompileStatic
class Main {
    static main(args) {
        FooSub foo = new FooSub()
        BarSub bar = new BarSub()
    }
}

@CompileStatic
class Foo<T> {
    void fooOne (T item) {}
    void fooMany(List<T> items) {
        items.each { T item -> fooOne(item) } // Compiles fine.
    }
}

@CompileStatic
class FooSub extends Foo<Integer> {}

@CompileStatic
class Bar<T extends Bar<T>>  {    
    void barOne (T item) {}
    void barMany(List<T> items) {

        items.each { T item -> barOne(item) } // Error:
        // Cannot find matching method Bar#barOne(java.lang.Object) !!!

        items.each { T item -> barOne(item as T) } // Error:
        // Expected parameter of type java.lang.Object but got T  !!!

        items.each { item -> barOne(item as T) } // Compiles fine - closure kNows about T

    }
    void barManyMore(List<T> items) {
        for (T item in items) { // Compiles fine.
            barOne(item) }
    }
}

@CompileStatic
class BarSub extends Bar<BarSub> {}

更新：
Groovy版本：2.4.5 JVM：1.7.0_80供应商：Oracle Corporation操作系统：Linux

更新
所以我之前没有注意到这个奇怪的错误 – org.codehaus.groovy.control.MultipleCompilationErrorsException：启动失败 – 我将发布完整输出：

~/grov/tests$groovyc generics.groovy 
org.codehaus.groovy.control.MultipleCompilationErrorsException: startup Failed:
generics.groovy: 27: Expected parameter of type java.lang.Object but got T
 @ line 27,column 19.
        items.each { T item -> barOne(item) } // Error:
                     ^

generics.groovy: 27: [Static type checking] - Cannot find matching method Bar#barOne(java.lang.Object). Please check if the declared type is right and if the method exists.
 @ line 27,column 29.
        items.each { T item -> barOne(item) } // Error:
                               ^

generics.groovy: 30: Expected parameter of type java.lang.Object but got T
 @ line 30,column 22.
           items.each { T item -> barOne(item as T) } // Error:
                        ^

3 errors

~/grov/tests$groovyc -v
Groovy compiler version 2.4.5
copyright 2003-2015 The Apache Software Foundation. http://groovy-lang.org/

更新

完整性的一些更多变通方法：
这些变通办法似乎有效：

Closure c = { T item -> barOne(item) }; items.each c // See comments by @tim_yates
    items.each ( { T item -> barOne(item) } as Closure)  // Casting to closure works too!

当类型是基于泛型T的类时,同样的问题也适用：

@CompileStatic
class Baz<T extends Baz<T>>  {
    List<T> getList() {
        return [new T(),new T()]
    }
}

@CompileStatic
class BazClient {
    void useBaz(Baz baz) {
        // baz.getList().each {Baz it -> println it} // Error
        Closure c = {Baz it -> println it}; baz.getList().each c  // works
        baz.getList().each ({Baz it -> println it} as Closure) // works
    }
}

解决方法

这是与泛型相关的 bugs之一,已在Groovy 2.4.6中修复.