implicit-conversion

问题 I have this Java class in a Jar file included as a dependency of an Scala program (like the Axis jar): class MyClass { private String[] someStrings; public String[] getSomeStrings() { return someStrings; } } In my Scala program I have a Java API that return an instance of MyClass instance of MyClass to my program in Scala: val myInstance = JavaAPI.getInstanceOfMyClass() Then I try to use the someStrings array in my Scala program but it's null (let say that it wasn't properly initialized) for

问题 The following code yields a compile time error: ' base::print ' : cannot access private member declared in class ' base_der ' However, I have made the member public in the derived class. Why doesn't this work? #include <iostream> using namespace std; class base { public: int i; void print(int i) { printf("base i\n"); } }; class base_der : private base { public: using base::print; }; int main() { // This works: base_der cls; cls.print(10); // This doesn't: void (base_der::* print)(int); print

问题 Background: Let's assume I've got the following class: class Wrapped<T> : IDisposable { public Wrapped(T obj) { /* ... */ } public static implicit operator Wrapped<T>(T obj) { return new Wrapped<T>(obj); } public void Dispose() { /* ... */ } } As you can see, it provides an implicit type conversion operator for T → Wrapped<T> . Ultimately, I would like to be able to use this class as follows: interface IX { /* ... */ } class X : IX { /* ... */ } ... IX plainIX = new X(); using (Wrapped<IX>

问题 Regarding the following compiler error: User-defined operator 'Foo.implicit operator Foo(Bar)' must be declared static and public What is the reason for this? Why must a user-defined conversion operator be public ? Give the following code, why wouldn't this conversion be legal: internal class Bar{} internal class Foo { private Bar _myBar; internal static implicit operator Bar(Foo foo) { return foo._myBar; } } I checked the C# Language Spec and the relevant section (10.10.3) didn't mention

问题 I discovered a strange behaviour of my program and after futher analysis, I was able to find that there is probably something wrong either in my C# knowledge or somewhere else. I beleive it's my mistake but I cannot find an answer anywhere... public class B { public static implicit operator B(A values) { return null; } } public class A { } public class Program { static void Main(string[] args) { A a = new A(); B b = a ?? new B(); //b = null ... is it wrong that I expect b to be B() ? } } The

问题 I'm working on a Windows Forms application, and it contains custom controls with methods that can potentially be called from threads other than the UI thread. So these methods therefore look a bit like this to prevent exceptions: public void DoSomeStuff() { if (InvokeRequired) { Invoke((Action)DoSomeStuff); } else { // Actually do some stuff. } } The explicit cast of the method group DoSomeStuff to an Action caught my attention, and so I've been looking into delegates and other related

问题 The Standard Library class template std::bitset<N> has a constructor (C++11 and onwards, unsigned long argument before C++11) constexpr bitset(unsigned long long) noexcept Contrary to many best-practice guidelines, this single-argument constructor is not marked as explicit . What is the rationale behind this? 回答1: Explicit construction The main objection against an explicit constructor is that copy-initialization from unsigned integers no longer works constexpr auto N = 64; std::bitset<N> b

问题 The Standard Library class template std::bitset<N> has a constructor (C++11 and onwards, unsigned long argument before C++11) constexpr bitset(unsigned long long) noexcept Contrary to many best-practice guidelines, this single-argument constructor is not marked as explicit . What is the rationale behind this? 回答1: Explicit construction The main objection against an explicit constructor is that copy-initialization from unsigned integers no longer works constexpr auto N = 64; std::bitset<N> b

问题 Is there an implicit method to convert scala.collection.mutable.StringBuilder to java.lang.StringBuilder? I am using a Java library (JCommander) in which one of the methods ( usage ) takes a java.jang.StringBuilder argument. 回答1: You can't start with a Scala StringBuilder and then obtain the Java version. You can, however, wrap a java.lang.StringBuilder in the Scala version. So: val jsb = new java.lang.StringBuilder(); val sb = new StringBuilder(jsb); // Do Scala-y stuff with sb JCommander

问题 This question already has an answer here : No viable conversion from std::function to bool (1 answer) Closed 3 years ago . Consider the following code. #include <functional> int main(void) { std::function<void()> f1; if (f1) { /* ok */ ... } bool b = f1; /* compile-error */ bool B = !f1; /* ok */ ... } std::function<> converts implicitly to bool in some circumstances but not in all of them. Assigning it to a bool -variable does not work, whereas the result of an operation or using it in an if