polymorphism

问题 I want to split a string delimited by commas and use the result as either a Seq or a Set : def splitByComma(commaDelimited: String): Array[String] = commaDelimited.trim.split(',') def splitByCommaAsSet(commaDelimited: String): Set[String] = splitByComma(commaDelimited).toSet def splitByCommaAsSeq(commaDelimited: String): Seq[String] = splitByComma(commaDelimited).toSeq val foods = "sushi,taco,burrito" val foodSet = splitByCommaAsSet(foods) // foodSet: scala.collection.immutable.Set[String] =

问题 I want to split a string delimited by commas and use the result as either a Seq or a Set : def splitByComma(commaDelimited: String): Array[String] = commaDelimited.trim.split(',') def splitByCommaAsSet(commaDelimited: String): Set[String] = splitByComma(commaDelimited).toSet def splitByCommaAsSeq(commaDelimited: String): Seq[String] = splitByComma(commaDelimited).toSeq val foods = "sushi,taco,burrito" val foodSet = splitByCommaAsSet(foods) // foodSet: scala.collection.immutable.Set[String] =

问题 I know this question has been asked a lot, but the usual answers are far from satisfying in my view. given the following class hierarchy: class SuperClass{} class SubClass extends SuperClass{} why does people use this pattern to instantiate SubClass: SuperClass instance = new SubClass(); instead of this one: SubClass instance = new SubClass(); Now, the usual answer I see is that this is in order to send instance as an argument to a method that requires an instance of SuperClass like here:

问题 I know this question has been asked a lot, but the usual answers are far from satisfying in my view. given the following class hierarchy: class SuperClass{} class SubClass extends SuperClass{} why does people use this pattern to instantiate SubClass: SuperClass instance = new SubClass(); instead of this one: SubClass instance = new SubClass(); Now, the usual answer I see is that this is in order to send instance as an argument to a method that requires an instance of SuperClass like here:

问题 I know this question has been asked a lot, but the usual answers are far from satisfying in my view. given the following class hierarchy: class SuperClass{} class SubClass extends SuperClass{} why does people use this pattern to instantiate SubClass: SuperClass instance = new SubClass(); instead of this one: SubClass instance = new SubClass(); Now, the usual answer I see is that this is in order to send instance as an argument to a method that requires an instance of SuperClass like here:

问题 I know this question has been asked a lot, but the usual answers are far from satisfying in my view. given the following class hierarchy: class SuperClass{} class SubClass extends SuperClass{} why does people use this pattern to instantiate SubClass: SuperClass instance = new SubClass(); instead of this one: SubClass instance = new SubClass(); Now, the usual answer I see is that this is in order to send instance as an argument to a method that requires an instance of SuperClass like here:

问题 let a = b in c can be thought as a syntactic sugar for (\a -> c) b , but in a typed setting in general it's not the case. For example, in the Milner calculus let a = \x -> x in (a True, a 1) is typable, but seemingly equivalent (\a -> (a True, a 1)) (\x -> x) is not. However, the latter is typable in System F with a rank 2 type for the first lambda. My questions are: Is let polymorphism a rank 2 feature that sneaked secretly in the otherwise rank 1 world of Milner calculus? The purpose of

问题 Can someone please explain how to ensure that the derived function is called from a pointer of type base to a derived object instead of the base function... Also, are the virtual and override keywords best practice to accomplish this? I had previously defined each overload with keyword friend in each class; but the base function was called for the base pointer to derived object. int main() { // contrived example ... base* ptr_derived = new derived(); std::cout << *ptr_derived; delete ptr

问题 I'm having an error message that tells me this: 'BankAccount.account' does not contain a definition for 'withdraw'. Here's my code: using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace BankAccounts { class account { protected string name; protected float balance; public account(string n, float b) { name = n; balance = b; } public void deposit(float amt) { balance -= amt; } public void display() { Console.WriteLine("Name: {0}. Balance: {1}.", name,

问题 My base class: class Item { protected: int count; string model_name; int item_number; public: Item(); void input(); } My derived Class: class Bed : public Item { private: string frame; string frameColour; string mattress; public: Bed(); void input(); } for now all my input function is trying to do is output which method is being used: void Item::input() { cout<<"Item input"<<endl; } void Bed::input() { cout<<" Bed Input"<<endl; } when I call the function in main I'd like the derived class