From d9c4308d9d96fcbfef3e85af44e1d3f3a95ed686 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@pdimov.com>
Date: Sat, 17 Jun 2017 19:14:47 +0300
Subject: [PATCH] Add list_size_mismatch which produces a better error message
 from mp_transform

---
 include/boost/mp11/algorithm.hpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/boost/mp11/algorithm.hpp b/include/boost/mp11/algorithm.hpp
index 996a61f..dbd3ef5 100644
--- a/include/boost/mp11/algorithm.hpp
+++ b/include/boost/mp11/algorithm.hpp
@@ -117,15 +117,19 @@ template<class... L> struct mp_same_size_2: mp_defer<mp_same_size_1, L...> {};
 
 #endif
 
+struct list_size_mismatch
+{
+};
+
 } // namespace detail
 
 #if BOOST_WORKAROUND( BOOST_MSVC, == 1900 ) || BOOST_WORKAROUND( BOOST_GCC, < 40800 )
 
-template<template<class...> class F, class... L> using mp_transform = typename mp_if<typename detail::mp_same_size_2<L...>::type, detail::mp_transform_impl<F, L...>>::type;
+template<template<class...> class F, class... L> using mp_transform = typename mp_if<typename detail::mp_same_size_2<L...>::type, detail::mp_transform_impl<F, L...>, detail::list_size_mismatch>::type;
 
 #else
 
-template<template<class...> class F, class... L> using mp_transform = typename mp_if<mp_same<mp_size<L>...>, detail::mp_transform_impl<F, L...>>::type;
+template<template<class...> class F, class... L> using mp_transform = typename mp_if<mp_same<mp_size<L>...>, detail::mp_transform_impl<F, L...>, detail::list_size_mismatch>::type;
 
 #endif