Typelist classes, algorithms and macros

Classes
struct	KMakeTypeList< T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18 >
struct	KTypeList< T, U >
class	KTypeListIndexOf
class	KTypeListLength
class	NullType

Detailed Description

Typelists are lists of C++ types of arbitrary length. They are used to carry type information at compile-time.

Internally, typelists are represented by the KTypeList template class. The KTypeList class uses the recursive structure of singly-linked lists which is common in functional programming languages:

• an empty list is of type KDE::NullType (the terminal marker)
• a one-element list with element T is of type KTypeList<T, KDE::NullType>.
• a two-element list with elements T and U is of type KTypeList<T, KTypeList<U, KDE::NullType> >.
• an N-Element list with the first element T and the remaining elements Rest is of type KTypeList<T, Rest>.

Note that the last element of a typelist is always KDE::NullType. Also note that this is only a convention, it is not enforced by anything. But if these rules are broken, the compile-time algorithms defined for typelists don't work.

To ease the definition of typelists, there are some macros which expand to nested KTypeList definitions. These macros have the form

K_TYPELIST_N(T1, T2, ..., TN)

where N is the number of types in the list (e.g. K_TYPELIST_3())

In addition to that, and also as the preferred way, there is the KMakeTypeList template which takes an arbitrary number of type arguments (up to 18) and exports a nested typedef called Result which equals a KTypeList with the list of provided arguments.

To work with typelists, several compile-time algorithms are provided:

• KTypeListLength: determine the number of elements in a typelist
• KTypeListIndexOf: find a given type in a typelist

For a detailed discussion about typelists, see the book "Modern C++ Design: Generic Programming and Design Patterns Applied" by Andrei Alexandrescu, and/or the Loki Library at http://sourceforge.net/projects/loki-lib/