![]() Naturally, this also extends to = default. Something that works with aggregates, but not with non-aggregates, is designated initializers (same cppreference page): Swan s. Swan is an aggregate, but Cow is not, because it has a user declared constructor. They are not aggregates, because they have private members. The first two, Dog and Horse, resemble your two versions of Dog. no virtual, private, or protected base classes.no user-declared or inherited constructors.no private or protected direct non-static data members.class type (typically, struct or union), that has.House does not define a default constructor: House(). From cppreference, only for C++20:Īn aggregate is one of the following types: Hi, I have a feeling that Im doing something wrong with my mocks: MockHouse inherits from House. Note how the two "default"s have slightly different meaning).Ī user declared constructor prevents a class from being an aggregate. 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". All data types compatible with the C language (POD types) are trivially default-constructible.Dog() = default is a user declared constructor (not to be confused with a user defined constructor). Objects with trivial default constructors can be created by using reinterpret_cast on any suitably aligned storage, e.g. Every non-static member of class type has a trivial default constructorĪ trivial default constructor is a constructor that performs no action.Every direct base of T has a trivial default constructor.T has no non-static members with brace-or-equal initializers.The constructor is not user-provided (that is, implicitly-defined or defaulted).performs no action) if all of the following is true: The default constructor for class T is trivial (i.e. T is a union and all of its variant members are const.T is a union with at least one variant member with non-trivial default constructor.T has a direct or virtual base which has a deleted destructor, or a destructor that is inaccessible from this constructor.T has a direct or virtual base which has a deleted default constructor, or it is ambiguous or inaccessible from this constructor.T has a member (without a brace-or-equal initializer) (since C++11), which has a deleted default constructor, or its default constructor is ambiguous or inaccessible from this constructor.T has a const member without user-defined default constructor or a brace-or-equal initializer (since C++11).T has a member of reference type without a brace-or-equal initializer. ![]() The implicitly-declared or defaulted default constructor for class T is undefined (until C++11) defined as deleted (since C++11) if any of the following is true: Deleted implicitly-declared default constructor That is, it calls the default constructors of the bases and of the non-static members of this class. If the implicitly-declared default constructor is not deleted or trivial, it is defined (that is, a function body is generated and compiled) by the compiler, and it has exactly the same effect as a user-defined constructor with empty body and empty initializer list. If some user-defined constructors are present, the user may still force the generation of the implicitly declared constructor with the keyword default If no user-defined constructors of any kind are provided for a class type ( struct, class, or union), the compiler will always declare a default constructor as an inline public member of its class. The default constructors are called during default initializations and value initializations. 4) Explicitly forcing the automatic generation of a default constructorĬlassName is the identifier of the enclosing class
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