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
If you define a class without any constructor, the compiler will synthesize a constructor for you (and that will be a default constructor — i.e., one that doesn’t require any arguments). If, however, you do define a constructor, (even if it does take one or more arguments) the compiler will not synthesize a constructor for … Read more
If you do not make a constructor, the default empty constructor is automatically created. If any constructor does not explicitly call a super or this constructor as its first statement, a call to super() is automatically added. Always.
As of Gson 2.3.1. Regardless of what the Gson documentation says, if your class doesn’t have an no-args constructor and you have not registered any InstanceCreater objects, then it will create an ObjectConstructor (which constructs your Object) with an UnsafeAllocator which uses Reflection to get the allocateInstance method of the class sun.misc.Unsafe to create your … Read more
Consider the following class: struct Foo { int i; }; This class is an aggregate, and you can create an instance with all three of these definitions: int main() { Foo f1; // i uninitialized Foo f2{}; // i initialized to zero Foo f3{42}; // i initialized to 42 } Now, let’s say that you … Read more
I personally find that using constructors is a much more common practice than knowing to use newInstance() and passing parameters. The factory method pattern is used fairly frequently in modern software development. So basically my question is, why does Google not want you to use constructors with parameters for Fragments? You answered your own question: … Read more
It’s wrong to say that a compiler-generated default constructor takes no action. It is equivalent to a user-defined constructor with an empty body and an empty initializer list, but that doesn’t mean it takes no action. Here is what it does: It calls the base class’es default constructor. It initializes the vtable pointer, if the … Read more