16.2.9 Runtime Type Identification (RTTI)
Run-time Type Identification, or RTTI, is a mechanism for
interrogating the type of an object at runtime. Such a mechanism is
useful for avoiding the dreaded switch-on-type technique used
before RTTI was incorporated into the language. Until recently,
some C++ compilers did not support RTTI, so it is necessary to
assume that it may not be widely available.
Switch-on-type involves giving all classes a method that returns a
special type token that an object can use to discover its own type. For
example:
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class Shape
{
public:
enum types { TYPE_CIRCLE, TYPE_SQUARE };
virtual enum types type () = 0;
};
class Circle: public Shape
{
public:
enum types type () { return TYPE_CIRCLE; }
};
class Square: public Shape
{
public:
enum types type () { return TYPE_SQUARE; }
};
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Although switch-on-type is not elegant, RTTI isn't particularly
object-oriented either. Given the limited number of times you ought to
be using RTTI, the switch-on-type technique may be reasonable.
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