Most vexing parse This is related to what is known as “C++’s most vexing parse”. Basically, anything that can be interpreted by the compiler as a function declaration will be interpreted as a function declaration. Another instance of the same problem: std::ifstream ifs(“file.txt”); std::vector<T> v(std::istream_iterator<T>(ifs), std::istream_iterator<T>()); v is interpreted as a declaration of function with … Read more
New answer (nine years later) There is now several overloads for Activator.CreateInstance that allow you to use non public constructors: Activator.CreateInstance(typeof(YourClass), true); true = use non public constructors. . Old answer Default constructors are private for a reason. The developer doesn’t make it private for fun. But if you still want to use the default … Read more
The terms default and implicit, when talking about a constructor have the following meaning: default constructor is a constructor that can be called with no arguments. It either takes no arguments or has default values for each of the arguments taken. implicit constructor is a term commonly used to talk about two different concepts in … Read more
This declares an explicit default constructor: struct A { explicit A(int a1 = 0); }; A a = 0; /* not allowed */ A b; /* allowed */ A c(0); /* allowed */ In case there is no parameter, like in the following example, the explicit is redundant. struct A { /* explicit is redundant. … Read more
It’s expected behaviour. There are two concepts, “default initialization” and “value initialization”. If you don’t mention any initializer, the object is “default initialized”, while if you do mention it, even as () for default constructor, the object is “value initialized”. When constructor is defined, both cases call default constructor. But for built-in types, “value initialization” … Read more
That is how Java works. The constructors of the parent classes are called, all the way up the class hierarchy through Object, before the child class’s constructor is called. Quoting from the docs: With super(), the superclass no-argument constructor is called. With super(parameter list), the superclass constructor with a matching parameter list is called. Note: … Read more
Reading explanation of members : explicit char_separator(const Char* dropped_delims, const Char* kept_delims = “”, empty_token_policy empty_tokens = drop_empty_tokens) explicit char_separator() The explicit keyword for the 1st constructor requires explicit creation of objects of char_separator type. What does the explicit keyword mean in C++? covers the explicit keyword very well. The explicit keyword for the 2nd … Read more
Yes: void foo(a::really::long::type::name arg = {}); To sum up the following standard definitions: This is list initialization. Depending of the type, aggregate initialization is performed or the object is value initialized, which in turn implies default initialized or zero initialized. Some “corner” cases are when the type is a specialization of std::initializer_list or when the … Read more
With standard reflection, no, but there is a library that can do it for you: objenesis. It’s specifically designed to instantiate classes without default constructors, and it’s used by other serialization libraries like xstream. Note: the constructor might not be called in these cases (but that’s presumably what you want).
A default (no-argument) constructor is automatically created only when you do not define any constructor yourself. If you need two constructors, one with arguments and one without, you need to manually define both.