Automatic two-phase init -- Krzysztof Ostrowski
Deferred initialisation for classes that inherit constructors, or Automatic two-phase init.
Deferred initialisation for classes that inherit constructors
by Krzysztof Ostrowski
From the article:
Constructor inheritance through using-declaration is a powerful technique that can be easily used to introduce pre-defined behaviour to custom types. As an example, consider a generic visitor design pattern implementation that is parametrised by the names of visitable types, and an unique tag that identifies given visitor template instance. Such an instance can be "mixed-in" into a custom type
Dby simply deriving from it... and inheriting its constructors to make it behave as it would be aVisitortemplate instance itself:struct D : Visitor< A // the tag , X, Y, Z // "list" of visitable types > { using Visitor::Visitor; };What if there is a need to run an "additional" initialisation code as it would be run in theDconstructor if one were there? Bjarne Stroustrup suggests member-initializers that do half of a work we would like to do here. While direct member initialisation sets required initial values for all the members (except bit field members), it does not offer a direct way to execute custom code that makes use of those members, the custom code that typically resides in the constructor's body.
This article presents a solution that enables injection of a custom code to be executed once all the non-static members are initialised.
