[boost] Re: Compile-time conditional function invocation

From: Jeff Mirwaisi (jeff_mirwaisi_at_[hidden])
Date: 2005-02-23 09:00:57

documentation, but just for completeness.

Given a type trait TT which you want to select upon.
Given a template function TF which you would like to
call only for types that TT selects from within
template function G.

We need a type which will delegate to TF, that doesn't
bind the template parameter types and is a first class
type (a holder)

template <typename T> void TF(T) {}

struct TF_holder
{
  typedef void result_type;
  template <typename T> result_type invoke(T t)
{return TF(t);}
};

template <typename U> void G(U u) { execute_if< TT< U
>::invoke< TF_holder >(u); }

G is the generic template function for all types, TF
is the conditionally targeted template function for
types for which TT is true.

Hope that helps.

Jeff Mirwaisi