constructor

问题 In javascript, the typical way to new up an object is by doing it like this: new Date() . But you can also do this: new (Date) . What is the difference and advantages of doing it the latter way? 回答1: There is no difference. The new operator takes a function reference. Like any other operator, the operand can have parentheses. The () after a new expression with no arguments are optional. However, if you have more a complicated expression inside the parentheses, they can change precedence

问题 I've never seen a single trait where properties and methods are private or protected. Every time I worked with traits I observed that all the properties and methods declared into any trait are always public only. Can traits have properties and methods with private and protected visibility too? If yes, how to access them inside a class/inside some other trait? If no, why? Can traits have constructor and destructor defined/declared within them? If yes, how to access them inside a class? If no,

问题 If initialise a unique_ptr like this: std::unique_ptr<Foo> i; i.reset( new Foo() ); but an exception is thrown from Foo::Foo() , the question is: what happens with the memory allocated? how does unique_ptr avoid it being leaked? is this something handled inside new operator? The destructor will certainly be called when the scope exits. Since the reset call is not invoked until new Foo() returns, it seems that this must be handled by new , by freeing the allocated memory when the exception

问题 Closed . This question is opinion-based. It is not currently accepting answers. Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. Closed 5 years ago . So I am a TA for a class at my University, and I have a bit of a disagreement about how to present datatypes for absolute beginner programmers (In which most never programmed before). My teacher tells students they must strictly use constructors to create primitive datatypes

问题 If initialise a unique_ptr like this: std::unique_ptr<Foo> i; i.reset( new Foo() ); but an exception is thrown from Foo::Foo() , the question is: what happens with the memory allocated? how does unique_ptr avoid it being leaked? is this something handled inside new operator? The destructor will certainly be called when the scope exits. Since the reset call is not invoked until new Foo() returns, it seems that this must be handled by new , by freeing the allocated memory when the exception

问题 If I want a constructor that is only accessible from child classes I can use the protected key word in the constructor. Now I want the opposite. My child class should have an constructor that can be accessed by its base class but not from any other class. Is this even possible? This is my current code. the problem is that the child classes have a public constructor. public abstract class BaseClass { public static BaseClass CreateInstance(DataTable dataTable) { return new Child1(dataTable); }

问题 I am trying a code about base class and member construction and destruction and I am confused about some order of constuctor and destructor, the output of this code is: Base1 constructor Member1 constructor Member2 constructor Derived1 constructor Member3 constructor Member4 constructor Derived2 constructor Derived2 destructor Member4 destructor Member3 destructor Derived1 destructor Member2 destructor Member1 destructor Base1 destructor See the first four line, but I fell the order should be

问题 When building a simple object in go, what's the difference between these alternatives? func NewGender(value string) Gender { return Gender{strings.TrimSpace(value)} } func NewGender(value string) *Gender { return &Gender{strings.TrimSpace(value)} } 回答1: The question is a really broad one, and it depends heavily on the rest of your API. So here are just some things you might need to consider when choosing one over another (in no particular order): Unnecessary pointers lead to more work for the

问题 When building a simple object in go, what's the difference between these alternatives? func NewGender(value string) Gender { return Gender{strings.TrimSpace(value)} } func NewGender(value string) *Gender { return &Gender{strings.TrimSpace(value)} } 回答1: The question is a really broad one, and it depends heavily on the rest of your API. So here are just some things you might need to consider when choosing one over another (in no particular order): Unnecessary pointers lead to more work for the

问题 I'm working on an object in C# where I need each instance of the object to have a unique id. My solution to this was simply to place a member variable I call idCount in the class and within the constructor I would have: objectID = idCount; idCount++; I thought that this would solve my problem but it seems that idCount never gets incremented even though the constructor gets called multiple times. For example if idCount = 1, the objectID for all the objects are still 1. Why doesn't idCount++