Reimplemented `Find` in terms of `ListIndex`

* `ListIndex` already implements the necessary partial template specializations for finding elements matching a predicate
* reimplemented `Cond` using `detail::find_variadic` as `Find` depends on `Apply` which in turn depends on `Cond`
** it is useful if core functionality such as the branched conditional `Cond` do not require higher order functionality such as `Find`
*** otherwise one can not use core functionality in the implementation of higher order functionality
* introduced `utility::predicate_guard` helper template
** checks a given value using a predicate and only forwards the value to the guarded function if this check is successful
** if check is unsuccessful it returns a surrogate value simmilar to `utility::predicate_assurance`

1 files changed, 22 insertions, 0 deletions

diff --git a/src/utility/predicate.h b/src/utility/predicate.h
index f06fcee..e84b18f 100644
--- a/src/utility/predicate.h
+++ b/src/utility/predicate.h
@@ -21,6 +21,28 @@ struct predicate_assurance {
 	>;
 };
 
+template <
+	template<typename...> class Function,
+	typename...                 Arguments
+>
+struct defer_eval {
+	typedef Function<Arguments...> type;
+};
+
+template <
+	template<typename> class Predicate,
+	template<typename> class Charge,
+	typename                 Surrogate
+>
+struct predicate_guard {
+	template <typename Value>
+	using check = Eval<If<
+		Eval<Predicate<Value>>,
+		defer_eval<Charge, Value>,
+		Surrogate
+	>>;
+};
+
 template <template<typename> class Predicate>
 struct predicate_negator {
 	template <typename Element>