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
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
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.
A type defined with enum class or enum struct is not a a class but a scoped enumeration and can not have a default constructor defined. The C++11 standard defines that your PinID pid = PinID(); statement will give a zero-initialization. Where PinID was defined as a enum class. It also allows enum types in … Read more
The functions exist, but can be inlined. When the compiler inlines the functions, it realizes they are no-ops, and there is no code generated. What the book is saying, is true to an extent, the notional functions are created by the compiler, for inline and direct calling. But the generated code is empty, so an … Read more
Dog() = default; is a user declared constructor (not to be confused with a user defined constructor). It is a defaulted default constructor. Typically you would use it when the class has other constructors but you still want the compiler to generate a default constructor (or rather a “defaulted default constructor”. This is C++ terminology … 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