From a8bec66b05eece7b8a39102fb1b0ba8f778eb9fe Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Thu, 19 Feb 2015 13:45:07 +0100
Subject: 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`

---
 src/utility/predicate.h | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

(limited to 'src/utility/predicate.h')

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>
-- 
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