Jack wrote: > I am not quite clear about calling the constructor of the based > class from the constructor of the derived class. > > For example, I should do something like this: > > type > TBaseClass = class(TObject) > public > color: TColor; > end; > > TDerivedClass = class(TBaseClass) > constructor Create; > destructor Destroy; > end; > > constructor TDerivedClass.Create; > begin > // is color variable available here?
Yes. Everything is in scope. Also see the following article. http://www.cs.wisc.edu/~rkennedy/field-defaults > inherited; > // other initialization steps > end; > > destructor TDerivedClass.Destroy; > begin > // other clean up steps > inherited; > end; > > However, sometimes I find that not calling inherited constructor > still works fine. Will this cause any trouble? It would cause the same amount of trouble as not calling any other inherited method. Decide to call an inherited method by the same criteria you use when deciding to call any other function or method. There is nothing special about calling inherited methods. It's just like calling any non-virtual method. Control jumps into the method, the statements get executes, and control returns to the caller. > Similarly, will not calling > the inherited destructor cause any memory leaks? If the destructor frees any memory, then not calling the destructor will cause leaks. You can't know whether a destructor frees any memory without looking at the code, or at least reading the class's documentation. > Also, before the inherited constructor is called, will the memebers > of the base class be accessible, e.g. the color variable in the above > code? I've answered your questions above, but I suspect I haven't answered the questions you really meant to ask. When you call a constructor to create an object, all the memory for that object gets allocated and initialized before _any_ line of code runs from any of the class's constructors. The object is fully created by the time any constructor runs. Likewise, memory for an object is not freed until the outermost destructor finishes running. All the memory inside an object is accessible from within any method of the class, including constructor and destructor methods. -- Rob _______________________________________________ Delphi mailing list -> [email protected] http://www.elists.org/mailman/listinfo/delphi
