Clang gives this warning message: <source>:12:16: warning: parentheses were disambiguated as redundant parentheses around declaration of variable named ‘num’ [-Wvexing-parse] Boo(num); // No default constructor ^~~~~ This is a most-vexing parse issue. Because Boo is the name of a class type and num is not a type name, Boo(num); could be either the construction of … Read more
You have to keep in mind that if you don’t provide an overloaded constructor, the compiler will generate a default constructor for you. That means, if you just have public class Foo { } The compiler will generate this as: public class Foo { public Foo() { } } However, as soon as you add … Read more
The trick is in C++14 8.4.2/5 [dcl.fct.def.default]: … A function is user-provided if it is user-declared and not explicitly defaulted or deleted on its first declaration. … Which means that C‘s default constructor is actually not user-provided, because it was explicitly defaulted on its first declaration. As such, C has no user-provided constructors and is … Read more
I originally posted this answer here, but here is a reprint since this isn’t the exact same question but has the same answer: FormatterServices.GetUninitializedObject() will create an instance without calling a constructor. I found this class by using Reflector and digging through some of the core .Net serialization classes. I tested it using the sample … Read more
By definition, default initialization is the initialization that occurs when no other initialization is specified; the C++ language guarantees you that any object for which you do not provide an explicit initializer will be default initialized (C++11 §8.5/11). That includes objects of type std::array<T, N> and T[N]. Be aware that there are types for which … Read more
If this class is only a utility class, you should make the class final and define a private constructor: public final class FilePathHelper { private FilePathHelper() { //not called } } This prevents the default parameter-less constructor from being used elsewhere in your code. Additionally, you can make the class final, so that it can’t … Read more
In the following, “auto-generated” means “implicitly declared as defaulted, but not defined as deleted”. There are situations where the special member functions are declared, but defined as deleted. The default constructor is auto-generated if there is no user-declared constructor (§12.1/5). The copy constructor is auto-generated if there is no user-declared move constructor or move assignment … Read more
There’s no reason that the compiler couldn’t add the constructor if you’ve added your own – the compiler could do pretty much whatever it wants! However, you have to look at what makes most sense: If I haven’t defined any constructor for a non-static class, I most likely want to be able to instantiate that … Read more
As of Kotlin 1.0.6, the kotlin-noarg compiler plugin generates synthetic default construtors for classes that have been annotated with selected annotations. If you use gradle, applying the kotlin-jpa plugin is enough to generate default constructors for classes annotated with @Entity: buildscript { dependencies { classpath “org.jetbrains.kotlin:kotlin-noarg:$kotlin_version” } } apply plugin: “kotlin-jpa” For Maven: <plugin> <artifactId>kotlin-maven-plugin</artifactId> … Read more
Neither of them. If you define it, it’s not the default. The default constructor is the no-argument constructor automatically generated unless you define another constructor. Any uninitialised fields will be set to their default values. For your example, it would look like this assuming that the types are String, int and int, and that the … Read more