cppannotations/yo/advancedtemplates/append.yo

The question of how to add an element to a typelist is handled using the same
    i(rule of thumb) as used for answering the previous questions: design a
recursive algorithm and implement the recursion through specializations.

    To append a new type to a typelist, the following algorithm can be used:
    itemization(
    it() The basic template is a struct expecting a typelist and a type to add
        to the typelist:
            verbinsert(APPEND)(advancedtemplates/examples/append.h)

    it() Adding tt(NullType):
        itemization(
        it() If the type to add is tt(NullType), and the original type is
            tt(NullType), the result itself is the tt(NullType):
        verbinsert(NULLTYPE)(advancedtemplates/examples/append.h)

    Note that the simple alternative:
        verb(
    template <typename TypeList>
    struct Append<TypeList, NullType>
    {
        typedef TypeList Result;
    };
        )
    is not a good idea, as it will match all types that are offered as the
template's first template type parameter. E.g., tt(Append<int, NullType>)
would be accepted, but would certainly not result in a tt(TypeList).
        it() When attempting to append tt(NullType) to an existing
            tt(TypeList), leave the tt(TypeList) as-is:
        verbinsert(ADDNULL)(advancedtemplates/examples/append.h)
        )

    it() Appending other types than tt(NullType):
        itemization(
        it() If the typelist itself is tt(NullType), the final typelist
        consists of the typelist containing the new type:
            verbinsert(NEWTYPE)(advancedtemplates/examples/append.h)

        it() Otherwise, the final typelist consists of the head of the initial
            typelist and the typelist resulting from appending the new type to
            the intial typelist's tail:
            verbinsert(TYPELIST)(advancedtemplates/examples/append.h)

            Once again: note that tt(typename) is required in front of
            tt(Append) (cf. section ref(DISTINGUISH))
        )
    )