generics

问题 I am writing the function that can catch exceptions of the certain type only. def myFunc[A <: Exception]() { try { println("Hello world") // or something else } catch { case a: A => // warning: abstract type pattern A is unchecked since it is eliminated by erasure } } What is the corrent way to bypass jvm type erasure in such case? 回答1: You could use ClassTag like in this answer. But I'd prefer this approach: def myFunc(recover: PartialFunction[Throwable, Unit]): Unit = { try { println("Hello

问题 I am currently trying to get some casting on generic types done. So the base idea is to have a method which accepts a generic Type and does different stuff depending on which type gets passed in. For simplicity reasons I will just showcase the use of float , bool and default The setup looks something like this (where T is a generic type defined by the class itself): protected T DoStuff(T value) { switch (value) { case float floatValue: float result = DoFloatStuff(floatValue); switch (result)

问题 I am currently trying to get some casting on generic types done. So the base idea is to have a method which accepts a generic Type and does different stuff depending on which type gets passed in. For simplicity reasons I will just showcase the use of float , bool and default The setup looks something like this (where T is a generic type defined by the class itself): protected T DoStuff(T value) { switch (value) { case float floatValue: float result = DoFloatStuff(floatValue); switch (result)

问题 I was going through TypeErasure topic at http://download.oracle.com/javase/tutorial/java/generics/erasure.html which says that compiler removes all information related to type parameters and type arguments within a class or method. Now considering the code below public class Box<T> { private T t; // lineA, T stands for "Type" public void add(T t) { // lineB this.t = t; // lineC } public T get() { // lineD return t; // lineE } } Now inside main method I have below code snippet Box<String> box1

问题 I was going through TypeErasure topic at http://download.oracle.com/javase/tutorial/java/generics/erasure.html which says that compiler removes all information related to type parameters and type arguments within a class or method. Now considering the code below public class Box<T> { private T t; // lineA, T stands for "Type" public void add(T t) { // lineB this.t = t; // lineC } public T get() { // lineD return t; // lineE } } Now inside main method I have below code snippet Box<String> box1

问题 I have a class that inherits from typing.Generic and passes in one TypeVar as the parameter. Later on in the code, I would like to: Statically (not at runtime) get the TypeVar parameter out from the class Alias it to another type variable Use that alias to type hint the return of a function Is there some way in Python that I can make this happen? The only piece I am missing is step 1, how to get the type parameter out of a type variable My Use Case from abc import ABC, abstractmethod from

问题 I have a trait GameStatistics that defines an add() method that takes a parameter and returns the sum of itself and the parameter. Implementations in subclasses should only accept instances of their own type as a parameter (or maybe also subtypes). I would like to use this add method to aggregate lists of GameStatistics , using Seq's reduce method. I have not been able to define this in Scala and make it compile. Below is one example that I tried plus its compile errors. The errors don't make

问题 I have a trait GameStatistics that defines an add() method that takes a parameter and returns the sum of itself and the parameter. Implementations in subclasses should only accept instances of their own type as a parameter (or maybe also subtypes). I would like to use this add method to aggregate lists of GameStatistics , using Seq's reduce method. I have not been able to define this in Scala and make it compile. Below is one example that I tried plus its compile errors. The errors don't make

问题 I have a method that writes one of my classes Foo , which is defined as Thrift, in Parquet form. import Foo import org.apache.spark.rdd.RDD import org.apache.thrift.TBase import org.apache.hadoop.mapreduce.Job import org.apache.parquet.hadoop.ParquetOutputFormat import org.apache.parquet.hadoop.thrift.ParquetThriftOutputFormat def writeThriftParquet(rdd: RDD[Foo], outputPath: String): Unit = { val job = Job.getInstance() ParquetThriftOutputFormat.setThriftClass(job, classOf[Foo])

问题 I wanted to store ListStyle in a property inside SupportOpts , so I added the <S> and where S: ListStyle to the struct declaration (from this answer). struct SupportOpts<S> where S: ListStyle { var title: String = "Placeholder" var listStyle: S = InsetGroupedListStyle() as! S /// had to put an `as! S` or else it couldn't compile } I can make an instance of it like this: let options: SupportOpts = SupportOpts( title: "Title", listStyle: InsetGroupedListStyle() ) But, when I remove