From e26621df352272688834361e7d026338cefb1372 Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Wed, 25 Feb 2015 18:47:56 +0100
Subject: Added `Cond` branch condition assertion * improves error messages in
 case no branch condition resolves to `true`

---
 src/conditional/cond.h | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

(limited to 'src/conditional')

diff --git a/src/conditional/cond.h b/src/conditional/cond.h
index 5f8014f..ca5e46d 100644
--- a/src/conditional/cond.h
+++ b/src/conditional/cond.h
@@ -12,12 +12,20 @@ namespace detail {
 template <typename Pair>
 using cond_predicate = IsTrue<Car<Pair>>;
 
+template <typename... Branches>
+struct select_cond_branch {
+	using type = Eval<detail::find_variadic<detail::cond_predicate, Branches...>>;
+
+	static_assert(
+		IsPair<type>::value,
+		"all branch conditions resolve to false"
+	);
+};
+
 }
 
 template <typename... Branches>
-using Cond = Cdr<Eval<
-	detail::find_variadic<detail::cond_predicate, Branches...>
->>;
+using Cond = Cdr<Eval<detail::select_cond_branch<Branches...>>>;
 
 template <
 	typename Condition,
-- 
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