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To erase the first occurrence of a specified tt(EraseType) from a tt(TypeList)
a recursive algorithm is used once again. The template meta program uses a
generic tt(Erase) struct and several specializations. The specializations
define a type tt(List) containing the resulting tt(TypeList) after the
erasure. Here is the algorithm:
itemization(
it() The foundation of the algorithm consists of a struct template
tt(Erase) expecting the type to erase and a tt(TypeList):
verbinclude(//ERASEPLAIN examples/erase.h)
it() If the typelist is empty, there's nothing to erase, and an empty
tt(TypeList) results:
verbinclude(//ERASEEMPTY examples/erase.h)
it() If the tt(TypeList)'s head matches the type to erase, then tt(List)
becomes a tt(TypeList) containing the original tt(TypeList)'s tail
types:
verbinclude(//ERASEHEAD examples/erase.h)
it() In all other cases the erase operation is applied to the
tt(TypeList)'s tail. This results in a tt(TypeList) to which the
orginal tt(TypeList)'s head must be prefixed. The tt(TypeList)
returned by the prefix operation is then returned as tt(Erase::List):
verbinclude(//ERASENEXT examples/erase.h)
)
Here is a statement showing how tt(Erase) can be used:
verbinclude(//ERASE examples/erase.cc)
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