Why does Ada have “tagged types” instead of classes?
(Tucker Taft responds): Someone recently asked me to explain the difference between the meaning of the term “class” in C++ and its meaning in Ada 95. Here is a synopsis of the answer: In C++, the term “class” refers to three different, but related things: • a language construct, that encapsulates the definitions of data members, member functions, nested types, etc.; • a particular kind of type, defined by a class construct (or by “struct” which is a special case of “class”); • a set of types consisting of a type and all of its derivatives, direct and indirect. In Ada 95, the term “class” refers only to the third of the above definitions. Ada 95 (and Ada 83) has three different terms for the concepts corresponding to the above three things: • a “package” encapsulates the definitions of types, objects, operations, exceptions, etc which are logically related. (The operations of a type defined immediately within the package where the type is declared are called, in Ada 95, the “primitive o
(Tucker Taft responds): Someone recently asked me to explain the difference between the meaning of the term “class” in C++ and its meaning in Ada 9X. Here is a synopsis of the answer: In C++, the term “class” refers to three different, but related things: * a language construct, that encapsulates the definitions of data members, member functions, nested types, etc.; * a particular kind of type, defined by a class construct (or by “struct” which is a special case of “class”); * a set of types consisting of a type and all of its derivatives, direct and indirect. In Ada 9X, the term “class” refers only to the third of the above definitions. Ada 9X (and Ada 83) has three different terms for the concepts corresponding to the above three things: * a “package” encapsulates the definitions of types, objects, operations, exceptions, etc which are logically related.
In C++, the term “class” refers to three different, but related things: a language construct, that encapsulates the definitions of data members, member functions, nested types, etc.; a particular kind of type, defined by a class construct (or by “struct” which is a special case of “class”); a set of types consisting of a type and all of its derivatives, direct and indirect. In Ada 95, the term “class” refers only to the third of the above definitions. Ada 95 (and Ada 83) has three different terms for the concepts corresponding to the above three things: • “package” encapsulates the definitions of types, objects, operations, exceptions, etc which are logically related. (The operations of a type defined immediately within the package where the type is declared are called, in Ada 95, the “primitive operations” of the type, and in some sense, define the “primitive” semantics of the type, especially if it is a private type.) • “type” is characterized by a set of values and a set of primitiv
(Tucker Taft responds): Someone recently asked me to explain the difference between the meaning of the term “class” in C++ and its meaning in Ada 9X. Here is a synopsis of the answer: In C++, the term “class” refers to three different, but related things: * a language construct, that encapsulates the definitions of data members, member functions, nested types, etc.; * a particular kind of type, defined by a class construct (or by “struct” which is a special case of “class”); * a set of types consisting of a type and all of its derivatives, direct and indirect. In Ada 9X, the term “class” refers only to the third of the above definitions. Ada 9X (and Ada 83) has three different terms for the concepts corresponding to the above three things: * a “package” encapsulates the definitions of types, objects, operations, exceptions, etc which are logically related. (The operations of a type defined immediately within the package where the type is declared are called, in 9X, the “primitive opera
