constructor

问题 struct B { int b1, b2; B(int, int); }; struct D : B { int d1, d2; // which is technically better ? D (int i, int j, int k, int l) : B(i,j), d1(k), d2(l) {} // 1st Base // or D (int i, int j, int k, int l) : d1(k), d2(l), B(i,j) {} // last Base }; Above is just pseudo code. In actual I wanted to know that does the order of calling base constructor matter ? Are there any bad behaviors (especially corner cases ) caused by any of the cases ? My question is on more technical aspect and not on

问题 I have a base class with a lot of __init__ arguments: def BaseClass(object): def __init__(self, a, b, c, d, e, f, ...): self._a=a+b self._b=b if b else a ... All the inheriting classes should run __init__ method of the base class. I can write a __init__() method in each of the inheriting classes that would call the superclass __init__ , but that would be a serious code duplication: def A(BaseClass): def __init__(self, a, b, c, d, e, f, ...): super(A, self).__init__(a, b, c, d, e, f, ...) def

问题 Apologies if this doesn't make any sense, I'm very new to Python! From testing in an interpreter, I can see that list() and [] both produce an empty list: >>> list() [] >>> [] [] From what I've learned so far, the only way to create an object is to call its constructor ( __init__ ), but I don't see this happening when I just type [] . So by executing [] , is Python then mapping that to a call to list() ? 回答1: No, Python does not call list() , or you could affect what type [] creates by

问题 How to inherit the constructor from a super class to a sub class? 回答1: Constructors are not inherited, you must create a new, identically prototyped constructor in the subclass that maps to its matching constructor in the superclass. Here is an example of how this works: class Foo { Foo(String str) { } } class Bar extends Foo { Bar(String str) { // Here I am explicitly calling the superclass // constructor - since constructors are not inherited // you must chain them like this. super(str); }

问题 How to inherit the constructor from a super class to a sub class? 回答1: Constructors are not inherited, you must create a new, identically prototyped constructor in the subclass that maps to its matching constructor in the superclass. Here is an example of how this works: class Foo { Foo(String str) { } } class Bar extends Foo { Bar(String str) { // Here I am explicitly calling the superclass // constructor - since constructors are not inherited // you must chain them like this. super(str); }

问题 This was asked slightly differently earlier but asking for a yes/no answer but I'm looking for the explanation that's missing from the book (Java Concurrency in Practice), of how this apparent big mistake would be exploited maliciously or accidentally. A final mechanism by which an object or its internal state can be published is to publish an inner class instance, as shown in ThisEscape in Listing 3.7. When ThisEscape publishes the EventListener, it implicitly publishes the enclosing

问题 I have the code: class A { public: A() = default; private: int i = 1; }; int main() { const A a; return 0; } It compiles fine on g++ (see ideone), but fails on clang++ with error: default initialization of an object of const type 'const A' requires a user-provided default constructor I reported this issue on LLVM bug-tracker and got it INVALID. I see it absolutly pointless to try to convince the clang developers. On the other side, I don't see the reason for such restriction. Can anyone

问题 How could I call the constructor of a class with call_user_func_array It is not possible to do : $obj = new $class(); call_user_func_array(array($obj, '__construct'), $args); because if the constructor has parameters, the new will fail. Constraint : I do not control the classes that I have to instantiate, nor can I modify them. Don't ask me why I want to do this crazy thing, this is a crazy test. 回答1: You can use reflection like: $reflect = new ReflectionClass($class); $instance = $reflect-

问题 In layman's terms, what's the difference between trivial types, standard layout types and PODs? Specifically, I want to determine whether new T is different from new T() for any template parameter T . Which of the type traits is_trivial , is_standard_layout and is_pod should I choose? (As a side question, can any of these type traits be implemented without compiler magic?) 回答1: I don't think it can be done in truly layman's terms, at least without a lot of extra explanation. One important

问题 In layman's terms, what's the difference between trivial types, standard layout types and PODs? Specifically, I want to determine whether new T is different from new T() for any template parameter T . Which of the type traits is_trivial , is_standard_layout and is_pod should I choose? (As a side question, can any of these type traits be implemented without compiler magic?) 回答1: I don't think it can be done in truly layman's terms, at least without a lot of extra explanation. One important