constructor

来源： https://stackoverflow.com/questions/55356837/what-is-the-difference-between-init-block-and-constructor-in-kotlin

来源： https://stackoverflow.com/questions/56965893/cannot-create-an-instance-of-class-viewmodel-in-kotlin

问题 As far as I'm aware, the following code: template<typename T> struct S { S<T>(); }; is well-formed, even though the <T> in the declaration of the constructor is redundant. However, on gcc trunk (but not on gcc10.2), with -std=c++20 this gives an error: error: expected unqualified-id before ')' token 3 | S<T>(); ^ The code compiles on clang trunk with -std=c++20 . Is this a bug, or is this a breaking change in c++20 that is yet to be implemented in all compilers? 回答1: There was a change, in

问题 I added some data in Cloud Firestore enter image description here in which I am having String title, String desc, String[] photos I want to get that data in MyClass.class so I provided Parameterized Constructor and Getter & Setters in the class. But the error said Converting to Arrays is not supported, please use Lists instead This is my code for logical part: FirebaseFirestore db = FirebaseFirestore.getInstance(); db.collection("gallery") .get() .addOnCompleteListener(new OnCompleteListener

问题 I added some data in Cloud Firestore enter image description here in which I am having String title, String desc, String[] photos I want to get that data in MyClass.class so I provided Parameterized Constructor and Getter & Setters in the class. But the error said Converting to Arrays is not supported, please use Lists instead This is my code for logical part: FirebaseFirestore db = FirebaseFirestore.getInstance(); db.collection("gallery") .get() .addOnCompleteListener(new OnCompleteListener

问题 In the Dart language tour for constructors it gives an example of a generative constructor: class Point { double x, y; Point(double x, double y) { // There's a better way to do this, stay tuned. this.x = x; this.y = y; } } Later it gives an example of a named constructor: class Point { double x, y; Point(this.x, this.y); // Named constructor Point.origin() { x = 0; y = 0; } } That led me to believe that when a constructor uses the same name as a class it is a generative constructor: Point

问题 I was trying to understand the usage of explicit keyword in c++ and looked at this question on SO What does the explicit keyword mean in C++? However, examples listed there (actually both top two answers) are not very clear regarding the usage. For example, // classes example #include <iostream> using namespace std; class String { public: explicit String(int n); // allocate n bytes to the String object String(const char *p); // initializes object with char *p }; String::String(int n) { cout<<

问题 For the following program: #include <vector> #include <iostream> int main() { std::vector<int> v = {"a", "b"}; for(int i : v) std::cout << i << " "; } clang prints 97 0 . The ascii value of 'a' is 97, but I don't fully understand the output. On the other hand, gcc throws an exception: terminate called after throwing an instance of 'std::length_error' what(): cannot create std::vector larger than max_size() so I assume it's using the 2 argument constructor that takes the size and default value

问题 I'm trying to pass 'this' to the constructor using std::make_shared Example: // headers class A { public: std::shared_ptr<B> createB(); } class B { private: std::shared_ptr<A> a; public: B(std::shared_ptr<A>); } // source std::shared_ptr<B> A::createB() { auto b = std::make_shared<B>(this); // Compiler error (VS11 Beta) auto b = std::make_shared<B>(std::shared_ptr<A>(this)); // No compiler error, but doenst work return b; } However this does not work properly, any suggestions how I can

问题 I am not able to autowire a bean while passing values in paramterized constructor. How to call the parameterized constructor using SpringBoot? @Component public class MainClass { public void someTask() { AnotherClass obj = new AnotherClass(1, 2); } } //Replace the new AnotherClass(1, 2) using Autowire? @Component public class AnotherClass { private int number,age; public AnotherClass(int number, int age) { super(); this.number = number; this.age = age; } } I want to autowire "AnotherClass"