提问人:Basel Shishani 提问时间:2/2/2016 最后编辑:Basel Shishani 更新时间:1/29/2018 访问量:869
泛型类型的闭包参数 - 异常
Closure parameter of Generic type - anomaly
问:
在下面的代码中,为什么 Groovy 似乎忽略了方法中提供的闭包参数的泛型类型声明:barMany
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
更新所以有一个我以前没有注意到的奇怪错误 - 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
为实现完整性,请提供以下更多解决方法: 这些解决方法似乎有效:
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!
当类型属于基于泛型 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
}
}
答:
0赞
jihor
1/29/2018
#1
这是在 Groovy 2.4.6 中修复的与泛型相关的错误之一。
评论
barMany
void barMany(List<T> items) { Closure c = { T it -> barOne(it) } ; items.each c }